US10294767B2 - Fluid transport systems for use in a downhole explosive fracturing system - Google Patents

Abstract

Explosive devices and assemblies are described herein for use in geologic fracturing. Components of energetic material used in the explosive devices can be initially separated prior to inserting the assembled system down a wellbore, then later combined prior to detonation. Some exemplary explosive units for insertion into a borehole for use in fracturing a geologic formation surrounding the borehole can comprise a casing comprising a body defining an internal chamber, a first component of an explosive positioned within the internal chamber of the casing, and an inlet communicating with the internal chamber through which a second component of the explosive mixture is deliverable into the internal chamber to comprise the explosive.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is the U.S. National Stage of International Application No. PCT/US2014/046742, filed Jul. 15, 2014, which was published in English under PCT Article 21(2), and which claims the benefit of U.S. Provisional Patent Application No. 61/846,528, filed Jul. 15, 2013, entitled “FLUID TRANSPORT SYSTEMS FOR USE IN A DOWNHOLE EXPLOSIVE FRACTURING SYSTEM,” which is incorporated by reference herein in its entirety.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Contract No. DE-AC52-06NA25396 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

PARTIES TO JOINT RESEARCH AGREEMENT

The research work described here was performed under a Cooperative Research and Development Agreement (CRADA) between Los Alamos National Laboratory (LANL) and Chevron under the LANL-Chevron Alliance, CRADA number LA05C10518-PTS-21.

FIELD

This application is related to systems and methods for use in geologic fracturing, such as in relation to accessing geologic energy resources.

BACKGROUND

Resources such as oil, gas, water and other materials may be extracted from geologic formations, such as deep shale formations, by creating fracture zones and resulting permeability within the formation, thereby enabling flow pathways for fluids (including liquids and/or gasses). For hydrocarbon based materials encased within geologic formations, this fracturing is typically achieved by a process known as hydraulic fracturing. Hydraulic fracturing is the propagation of fractures in a rock layer using a pressurized fracturing fluid. This type of fracturing is done from a wellbore drilled into reservoir rock formations. The energy from the injection of a pressurized fracturing fluid creates new channels in the rock which can increase the extraction rates and ultimate recovery of hydrocarbons. The fracture width may be maintained after the injection is stopped by introducing a proppant, such as grains of sand, ceramic, or other particulates into the injected fluid. Additionally, by its nature, the direction and distance a hydraulic fracture travels is mainly dependent on the direction of the maximum principle (in-situ) stress in the reservoir. Although this technology has the potential to provide access to large amounts of efficient energy resources, the practice of hydraulic fracturing has been restricted in parts of the world due to logistical or regulatory constraints. Therefore, a need exists for alternative fracturing methods.

SUMMARY

Explosive devices and assemblies are described herein for use in geologic fracturing. Components of energetic material used in the explosive devices can be initially separated prior to inserting the assembled system down a wellbore, then later combined prior to detonation. Some exemplary explosive units for insertion into a borehole for use in fracturing a geologic formation surrounding the borehole can comprise a casing comprising a body defining an internal chamber, a first component of an explosive positioned within the internal chamber of the casing, and an inlet communicating with the internal chamber through which a second component of the explosive mixture is deliverable into the internal chamber to comprise the explosive.

In some embodiments, the casing comprises a passageway communicating from a source of the second component at the surface of the wellbore to the inlet.

In some embodiments, the first component comprises a liquid permeable oxidizer. For example, the first component can comprise a particulate solid material or a sponge-like material and the second component can comprise a liquid fuel.

In some embodiments, the explosive unit further comprises a remotely actuated vent communicating with the internal chamber.

In some embodiments, the casing comprises first and second opposed end caps and the inlet tube extends through the first end cap, through the internal chamber, and through the second end cap. The inlet can comprise a tube with an inline outlet communicating with the internal chamber and an inlet communicating with a source of the second component at a location that is remote from the explosive unit and can also comprise an outlet that communicates with the internal chamber.

Some explosive systems comprise a first elongated casing having a tubular body, first and second longitudinal end caps, and defining a first internal chamber, and further comprise a second elongated casing having a tubular body, first and second longitudinal end caps, and defining a second internal chamber, wherein the first and second casings are mechanically coupled together in axial alignment. Each of the first and second casings comprising a first component of an explosive located within the respective internal chamber of the casing. The system further comprises an inlet tube communicating with the first and second internal chambers of the respective first and second casings, wherein the inlet tube is operable to deliver a second component of the explosive into the first and second internal chambers so as to combine with the first component of the explosive to comprise the explosive.

In some embodiments, the inlet tube comprises a first outlet communicating with the first internal chamber of the first casing and a second outlet communicating with the second internal chamber of the second casing.

In some embodiments, the inlet tube comprises a first section extending from the first casing, a second section extending into the second casing, and an inlet tube coupler that couples the first and second inlet tube sections together between the first and second casings. In some such embodiments, a first end of the inlet tube is coupled to a liquid fuel source configured to supply the liquid fuel through the inlet tube into the first and second internal chambers. The first end of the inlet tube can be further coupled to a vacuum pump configured to create a vacuum within the first and second internal chambers so as to draw the liquid fuel into the internal chambers.

In some embodiments, the system also comprises an outlet vent tube communicating with the first and second internal chambers and operable to vent fluid from the first and second internal chambers when the second component of the explosive mixture is delivered into the first and second internal chambers. In some of these embodiments, the inlet tube has no outlet within the first casing and has an outlet within the internal chamber of the second casing, and the system comprises a passageway communicating from the second internal chamber to the first internal chamber. The second component of the explosive can be configured to flow along the inlet tube through the first casing, flow out of the outlet of the inlet tube into the internal chamber of the second casing, flow into passageway from the second internal chamber, and flow out of the passageway into the first internal chamber.

In some embodiments, the outlet tube comprises a first section extending from the second casing, a second section extending into the first casing, and an outlet tube coupler that couples the first and second outlet tube sections together between the first and second casings.

In some embodiments, the system comprises a vent coupled to the internal chambers of the first and second casings, wherein the first component comprises a permeable oxidizer and the second component comprises a liquid fuel, and wherein the system comprises a pump that pumps the liquid through the inlet tube, into the internal chamber of the second casing, and through the outlet tube into the first casing, and wherein the vent vents the internal chambers as the liquid flows into the first and second chambers.

Exemplary methods can comprise: inserting an explosive assembly into a wellbore, the assembly comprising at least one explosive unit having a casing with a first component of an explosive within the casing; and then flowing a second component of the explosive into the inserted casing to comprise the explosive; and then detonating the explosive to fracture the geologic structure surrounding the borehole and casing.

In some embodiments, the explosive assembly can comprise a first explosive unit coupled to a second explosive unit, wherein each explosive unit comprises a casing with a first component of an explosive located within the casing; and flowing a second component of the explosive into the inserted casings of the first and second explosive units to comprise the explosive.

In some embodiments, the act of flowing the second component comprises flowing the second component into the first explosive unit from a location outside of the entrance opening to the wellbore.

In some embodiments, the act of flowing comprises venting the casing and pumping the second component into the vented casing, and the method further comprises closing the vent following flowing of the second component into the casing.

In some embodiments, the act of flowing comprises drawing a vacuum within the casing, coupling a supply of the second component to the casing, and using the vacuum in the casing to draw the second component into the casing.

The foregoing and other features and advantages of the disclosure will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a geologic formation accessed with a wellbore.

FIG. 2 is an enlarged view of a portion ofFIG. 1 showing a proximal portion of an exemplary tool string being inserted into the wellbore.

FIG. 3 is a cross-sectional view of a tool string portion positioned in a curved portion of a wellbore.

FIG. 4 is a cross-sectional view of a tool string distal portion having a tractor mechanism for pulling through the wellbore.

FIG. 5 is a cross-sectional view of a tool string completely inserted into a wellbore and ready for detonation.

FIG. 6 is a cross-sectional view of an exemplary unit of a tool string in a wellbore, taken perpendicular to the longitudinal axis.

FIG. 7 is a perspective view of an exemplary tool string portion.

FIGS. 8A-8G are schematic views of alternative exemplary tool strings portions.

FIG. 9 is a perspective view of an exemplary unit of a tool string.

FIG. 10 is a partially cross-sectional perspective view of a portion of the unit ofFIG. 9.

FIG. 11 is an enlarged view of a portion ofFIG. 10.

FIG. 12 is an exploded view of an exemplary explosive system.

FIGS. 13 and 14A are cross-sectional views of the system ofFIG. 12 taken along a longitudinal axis.

FIGS. 14B-14D are cross-sectional views showing alternative mechanical coupling systems.

FIG. 15 is a diagram representing an exemplary detonation control module.

FIGS. 16A-16C are perspective views of one embodiment of a detonation control module.

FIG. 17 is a circuit diagram representing an exemplary detonation control module.

FIG. 18 is a flow chart illustrating an exemplary method disclosed herein.

FIG. 19 is a partially cross-sectional perspective view of a theoretical shock pattern produced by a detonated tool string.

FIGS. 20 and 21 are vertical cross-sectional views through a geologic formation along a bore axis, showing rubbilization patterns resulting from a detonation.

FIG. 22A is a schematic representing high and low stress regions in a geologic formation a short time after detonation.

FIG. 22B is a schematic showing the degree of rubbilization in the geologic formation a short time after detonation.

FIG. 22C is a schematic illustrating different geologic layers present in the rubbilization zone.

FIG. 23 is a graph of pressure as a function of distance from a bore for an exemplary detonation.

FIG. 24 is a graph showing exemplary gas production rates as a function of time for different bore sites using different methods for fracturing.

FIG. 25 is a graph showing exemplary total gas production as a function of time for different bore sites using different methods for fracturing.

FIG. 26A illustrates detonation planes resulting from the ignition of pairs of propellant containing tubes substantially simultaneously along their entire length and an intermediate pair of high explosive containing tubes from their adjacent ends.

FIG. 26B illustrates an exemplary arrangement of interconnected alternating pairs of propellant and high explosive containing tubes.

FIG. 27 is a cross-sectional view of an exemplary explosive unit having a preloaded permeable material and an inlet tube to receive a liquid to mix with the permeable material.

FIG. 28 is a diagram showing a portion of an exemplary explosive system having an inlet tube extending through plural explosive units for delivery of a liquid material into the explosive units.

FIG. 29 is a diagram showing another explosive system having an inlet tube extending through plural explosive units for delivery of a liquid material into the explosive units.

FIG. 30 is a diagram showing a portion of yet another exemplary explosive system having an inlet tube extending through plural explosive units for delivery of a liquid material into a distal explosive unit, and outlet tubes for conducting the liquid material proximally through the explosive units and venting the explosive units.

FIG. 31 is a diagram showing an exemplary explosive system having an inlet tube extending through plural explosive units for delivery of a liquid material into a distal explosive unit, and outlet tubes for conducting the liquid material proximally through the explosive units and venting the explosive units.

DETAILED DESCRIPTIONI. Introduction

Although the use of high energy density (HED) sources, such as explosives, for the purpose of stimulating permeability in hydrocarbon reservoirs has been previously investigated, the fracture radius away from the borehole with such technologies has never extended for more than a few feet radially from the borehole. Permeability stimulation in tight formations is currently dominated by the process known as hydraulic fracturing. The term “hydraulic fracturing” is used herein to include any type of geologic fracturing that utilizes pressurized fluid. The term “fluid” as used herein includes any flowable material, including liquids, gasses, solid particles, and combinations thereof. With hydraulic fracturing, fluid is pumped into the reservoir via a perforated wellbore to hydraulically fracture the rock providing a limited network of propped fractures for hydrocarbons to flow into a production well. The fracturing extent and direction are dependent on the in-situ formation stress and in particular the maximum principle formation stress.

Past investigations and present practice of stimulating permeability in tight formations do not take full advantage of the information gained from detailed analysis of both the formation properties and the customization of a HED system to create optimal permeability zones. Some systems disclosed herein take into account best estimates of the shock wave behavior in the specific geologic formation and can be geometrically configured and adjusted in detonation time to enhance the beneficial mixing of multiple shock waves from multiple sources to extend the damage/rubblization of the rock to economic distances. Shock waves travel with different velocities and different attenuation depending on physical geologic properties. These properties include strength, porosity, density, hydrocarbon content, water content, saturation and a number of other material attributes.

As such, explosive systems, compositions, and methods are disclosed herein which are designed to be used to fracture geologic formations to provide access to energy resources, such as geothermal and hydrocarbon reservoirs. Some disclosed methods and systems, such as those for enhancing permeability in tight geologic formations, involve the beneficial spacing and timing of HED sources, which can include explosives and specially formulated propellants. In some examples, the disclosed methods and systems include high explosive (HE) systems, propellant (PP) systems, and other inert systems. The beneficial spacing and timing of HED sources provides a designed coalescence of shock waves in the geologic formation for the designed purpose of permeability enhancement.

Beneficial spacing of the HED sources can be achieved through an engineered system designed for delivery of the shock to the geologic formations of interest. A disclosed high fidelity mobile detonation physics laboratory (HFMDPL) can be utilized to control the firing of one or more explosive charges and/or to control the initiation of one or more propellant charges, such as in a permeability enhancing system.

Some advantages over conventional hydrofracturing which can be attributed to the HED compositions include the following: (1) the resulting rubblized zone around the stimulated wellbore can comprise a substantially 360° zone around the wellbore, as compared to traditional hydrofractures which propagate in a single plane from the wellbore in the direction of the maximum principle stress in the rock or extents along a pre-existing fracture; (2) the useful rubblizaton zone can extend to a significant radius from the bore, such as a radius or average radius, expected to be at least a three times improvement over a continuous charge of equal yield, such as a six times improvement; and (3) the ability to generate explosions tailored to specific geologic profiles, thereby directing the force of the explosion radially away from the bore to liberate the desired energy resource without resulting in substantial pulverization of geologic material immediately adjacent to the wellbore, which can clog flow pathways thus reducing the production of energy or resources.

Various exemplary embodiments of explosive devices, systems, methods and compositions are described herein. The following description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the disclosure in any way. Various changes to the described embodiments may be made in the function and arrangement of the elements described herein without departing from the scope of the invention.

II. Terms and Abbreviations

i. Terms

As used herein, the term detonation (and its grammatical variations) is not limited to traditional definitions and instead also includes deflagration and other forms of combustion and energetic chemical reactions.

As used herein, the term detonator is used broadly and includes any device configured to cause a chemical reaction, including explosive detonators and propellant initiators, igniters and similar devices. In addition, the term detonation is used broadly to also include detonation, initiation, igniting and combusting. Thus a reference to detonation (e.g. in the phrase detonation control signal) includes detonating an explosive charge (if an explosive charge is present) such as in response to a fire control signal and initiating the combustion of a propellant charge (if a propellant charge is present) such as in response to a fire control signal.

In addition a reference to “and/or” in reference to a list of items includes the items individually, all of the items in combination and all possible sub-combinations of the items. Thus, for example, a reference to an explosive charge and/or a propellant charge means “one or more explosive charges”, “one or more propellant charges” and “one or more explosive charges and one or more propellant charges.

As used in this application, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” generally means electrically, electromagnetically, and/or physically (e.g., mechanically or chemically) coupled or linked and does not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language.

It is further to be understood that all sizes, distances and amounts are approximate, and are provided for description. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including explanations of terms, will control.

ii. Abbreviations

• • Al: Aluminum
  • CL-20: 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane
  • DAAF: diaminoazoxyfurazan
  • ETN: erythritol tetranitrate
  • EGDN: ethylene glycol dinitrate
  • FOX-7: 1,1-diamino-2,2-dinitroethene
  • GAP: Glycidyl azide polymer
  • HMX: octogen, Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine
  • HNS: hexanitrostilbene
  • HE: high explosive
  • HED: high energy density
  • HFMDPL: High Fidelity Mobile Detonation Physics Laboratory
  • LAX-112: 3,6-diamino-1,2,4,5-tetrazine-1,4-dioxide
  • NG: nitroglycerin
  • NTO: 3-nitro-1,2,4-triazol-5-one
  • NQ: nitroguanidine
  • PETN: pentaerythritol tetranitrate
  • PP: propellant(s)
  • RDX: cyclonite, hexogen, 1,3,5-Trinitro-1,3,5-triazacyclohexane, 1,3,5-Trinitrohexahydro-s-triazine
  • TAGN: triaminoguanidine nitrate
  • TNAZ: 1,3,3-trinitroazetidine
  • TATB: triaminotrinitrobenzene
  • TNT: trinitrotoluene

III. Exemplary Systems

Disclosed are systems for enhancing permeability of a tight geologic formation, such as closed fractures or unconnected porosity of a geologic formation. In some examples, a system for enhancing permeability includes at least one high explosive (HE) system. For example, an HE system can include one or more HE, such as a cast curable HE. Desirable characteristics of an HE system can include one or more of the following: the HE system is environmentally benign; the HE is safe to handle, store and utilize in all required configurations, and in industrialized wellbore environments; the HE has a high total stored energy density (e.g. total stored chemical energy density), such as at least 8 kJ/cc, at least 10 kJ/cc, or at least 12 kJ/cc; and the HE is highly non-ideal. A non-ideal HE can be defined, for example, as an HE in which 30% to 40% or more of the meta-stably stored chemical energy is converted to HE hot product gases after the detonation front (shock front) in a deflagrating Taylor Wave. Further details of HE chemical compositions are described below (see, for example, Section VIII).

Some exemplary systems for enhancing permeability include one or more propellant (PP) systems, such as one or more PP systems in the axial space along the bore between the HE systems, which can add more useable energy to the system and/or help direct energy from the HE systems radially into the geologic formation rather than axially along the bore, without defeating the goal of wave interaction sought through the axial spatial separation of charges. The PP systems can pressurize the bore and/or add uncompressible or low-compressibility material in the bore between the HE systems the helps high-pressure energy from the HE systems from travelling axially along the bore. The PP systems can further increase or sustain high pressure in the annular region of the bore between the outside of the HE systems and the bore walls. Sustaining a high pressure in the bore helps to support the radially outwardly traveling wave of energy, causing the region of significant fracture to be extended radially. As used herein, a bore is any hole formed in a geologic formation for the purpose of exploration or extraction of natural resources, such as water, gas or oil. The term bore may be used interchangeably with wellbore, drill hole, borehole and other similar terms in this application.

The pressure generated by the combustion products of the PP confined in the bore is a contributor to increasing the radial travel of HE energy waves. Desirable characteristics of an exemplary PP system include one or more of the following: the PP system is environmentally benign; the material is safe to handle, store and utilize in all required configurations, and in industrialized wellbore environments; and the PP deflagrates without transitioning into a detonation within the context of the separately timed geometry- and material-specific HE. The active material in a PP system can comprise one or more of variety of materials, including: inert materials, such as brine, water, and mud; and energetic materials, such as explosive, combustible, and/or chemically reactive materials. These materials can be environmentally benign and safe to handle, store and utilize in required configurations and in industrialized bore environments. It is contemplated that the PP material may be fluid, semi-fluid or solid in nature. Desirably, the PP systems comprise or produce a product that has low compressibility. Further details of exemplary propellants are described below (see, for example, Section VIII).

Optimized geometry- and material-specific configurations of the disclosed systems enable carefully timed, multiple detonation events along HE-PP strings within the bore environment. The disclosed systems optimize the interaction of multiple shock waves and rarefaction waves within the surrounding formation, thereby producing 360 degree rubblization zones, which can be at least three to four times the radius produced by an equivalent radius of a continuous detonating column of the same HE. Further, optimized material layers between the bore wall and radially outer surfaces of the HE-PP string can minimize the amount of energy wasted on crushing/pulverizing geologic material near the bore/epicenter, thereby optimizing the transition of available energy into the geologic material in a manner that maximizes useful rubblization effects and maximizes flow channels through the rubblized material.

FIG. 1 shows a cross-section of an exemplarygeologic formation10 that comprises atarget zone12 comprising an energy resource, which is positioned below another geologic layer, oroverburden14. Anexemplary bore16 extends from arig18 at the surface, through theoverburden14, and into thetarget zone12. Thebore16 can be formed in various configurations based on the shape of the geologic formations, such as by using known directional drilling techniques. In the illustrated example, thebore16 extends generally vertically from arig18 through theoverburden14 and then curves and extends generally horizontally through thetarget zone12. In some embodiments, thebore16 can extend through two ormore target zones12 and/or through two or more overburdens14. In some embodiments, the bore can be generally vertical, angled between vertical and horizontal, partially curved at one or more portions, branched into two or more sub-bores, and/or can have other known bore configurations. In some embodiments, the target zone can be at or near the surface and not covered by an overburden. Thetarget zone12 is shown having a horizontal orientation, but can have any shape or configuration.

As shown inFIG. 2, after thebore16 is formed, anexplosive tool string20 can be inserted into the bore. Thestring20 can comprise one ormore units22 coupled in series via one ormore connectors24. Theunits22 can comprise explosive units, propellant units, inert units, and/or other units, as described elsewhere herein. Theunits22 andconnectors24 can be coupled end-to-end in various combinations, along with other components, to form theelongated string20. Thestring20 can further comprise aproximal portion26 coupling the string to surface structures and control units, such as to support the axial weight of the string, to push the string down the bore, and/or to electrically control theunits22.

As shown inFIG. 3, one or more of theconnectors24 can compriseflexible connectors28 and one or more of theconnectors24 can compriserigid connectors30. Theflexible connectors28 can allow the string to bend or curve, as shown inFIG. 3. In the example ofFIG. 3, every other connector is aflexible connector28 while the other connectors are rigid orsemi-rigid connectors30. Inother strings20, the number and arrangement of flexible and rigid connectors can vary. Theflexible connectors28 can be configured to allowadjacent units22 to pivot off-axis from each other in any radial direction, whereas therigid connectors30 can be configured to maintainadjacent units22 in substantial axial alignment. The degree of flexibility of theflexible connectors28 can have varying magnitude. In some embodiments, thestring20 can comprising at least one flexible connector, or swivel connector, and configured to traverse a curved bore portion having a radius of curvature of less than 500 feet. Additional instances of flexible connectors at smaller intervals apart from each other can further reduce the minimum radius of curvature traversable by the string. Furthermore, each joint along the string can be formed with a given amount of play to allow additional flexing of the string. Joints can be formed using threaded connected between adjoining units and connectors and are designed to allow off-axis motion to a small degree in each joint, as is describe further below.

As shown inFIG. 3, the distal end of thestring20 can comprise a nose-cone32 or other object to assist the string in traveling distally through thebore16 with minimal resistance. In some embodiments, as shown inFIG. 4, the distal end of thestring20 can comprise atractor34 configured to actively pull the string through thebore16 via interaction with the bore distal tounits22.

FIG. 5 shows anexemplary string20 fully inserted into abore16 such thatunits22 have passed the curved portion of the bore and are positioned generally in horizontal axial alignment within thetarget zone12. In this configuration, thestring20 can be ready for detonation.

FIG. 6 shows a cross-section of anexemplary unit22 positioned within abore16. Theunit22 contains amaterial36, which can comprise a high energy explosive material, a propellant, brine, and/or other materials, as described herein. Afluid material38, such as brine, can fill the space between the outer surface of the string20 (represented by theunit22 inFIG. 6) and the inner wall of thebore16. The inner diameter of theunit22, D1, the outer diameter of the unit and thestring20, D2, and the diameter of the bore, D3, can vary as described herein. For example, D1 can be about 6.5 inches, D2 can be about 7.5 inches, and D3 can be about 10 inches.

Eachunit22 can comprise an HE unit, a PP unit, an inert unit, or other type of unit. Two or moreadjacent units22 can form a system, which can also include one or more of the adjoining connectors. For example,FIG. 7 shows anexemplary string20 comprising a plurality ofHE units40 and a plurality ofPP units42. Each adjacent pair ofHE units40 and theintermediate connector24 can comprise anHE system44. Each adjacent pair ofPP units42 and the three adjoining connectors24 (the intermediate connector and the two connectors at the opposite ends of the PP units), can comprise aPP system46. In other embodiments, any number ofunits20 of a given type can be connected together to from a system of that type. Furthermore, the number and location of connectors in such system can vary in different embodiments.

Connectors24 can mechanically couple adjacent units together to support the weight of thestring20. In addition, some of theconnectors24 can comprise electrical couplings and/or detonator control modules for controlling detonation of one or more of the adjacent HE or PP units. Details of exemplary detonator control modules are described below.

In some embodiments, one or more HE systems in a string can comprise a pair of adjacent HE units and a connector that comprises a detonator control module configured to control detonation of both of the adjacent HE units of the system. In some embodiments, one or more HE systems can comprise a single HE unit and an adjacent connector that comprises a detonator control module configured to control detonation of only that single HE unit.

Each unit can be independently detonated. Each unit can comprise one or more detonators or initiators. The one or more detonators can be located anywhere in the unit, such as at one or both axial ends of the unit or intermediate the axial ends. In some embodiments, one or more of the units, such as HE units, can be configured to be detonated from one axial end of the unit with a single detonator at only one axial end of the unit that is electrically coupled to the detonator control module in an adjacent connector.

In some units, such as PP units, the unit is configured to be detonated or ignited from both axial ends of the unit at the same time, or nearly the same time. For example, a PP unit can comprise two detonators/igniters/initiators, one at each end of the PP unit. Each of the detonators of the PP unit can be electrically coupled to a respective detonator control module in the adjacent connector. Thus, in some embodiments, one or more PP systems in a string can comprise a pair of adjacent PP units and three adjacent connectors. The three adjacent connectors can comprise an intermediate connector that comprises a detonator control module that is electrically coupled to and controls two detonators, one of each of the two adjacent PP units. The two connectors at either end of the PP system can each comprise a detonator control module that is electrically coupled to and controls only one detonator at that end of the PP system. In PP systems having three or more PP units, each of the intermediate connectors can comprise detonator control modules that control two detonators. In PP systems having only a single PP unit, the PP system can comprise two connectors, one at each end of the PP unit. In embodiments having detonators intermediate to the two axial ends of the unit, the detonator can be coupled to a detonation control module coupled to either axial end of the unit, with wires passing through the material and end caps to reach the detonation control module.

FIGS. 8A-8G showseveral examples strings20 arranged in different manners, with HE unit detonators labeled as De and PP unit detonators labeled as Dp.FIG. 8A shows a portion of a string similar to that shown inFIG. 7 comprising alternating pairs ofHE systems44 andPP systems46.FIG. 8B shows a portion of a string having HEsystems44 and PP systems as well asinert units48 positioned therebetween. Any number ofinert units48 can be used along thestring20 to position the HE units and PP units in desired positions relative to the given geologic formations. Instead of inert units48 (e.g., containing water, brine or mud), or in addition to theinert units48, units positioned between the HE units and/or the PP units in a string can comprise units containing non-high energy explosives (e.g., liquid explosives). Any combination of inert units and non-high energy units can be includes in a string in positions between the HE units and/or PP units, or at the proximal and distal ends of a string.

FIG. 8C shows a portion of astring20 comprising a plurality of single-unit HE systems50 alternating with single-unit PP systems52. In this arrangement, each connector is coupled to one end of a HE unit and one end of a PP unit. Some of these connectors comprise a detonation control module configured to control only a PP detonator, while others of these connectors comprise a detonation control module configured to control one PP detonator and also control one HE detonator.FIG. 8D shows an exemplary single-unit PP system52 comprising a connector at either end.FIG. 8E shows an exemplary single-unit HE system50 comprising a single connector at one end. The single-unit systems50,52, the double-unit systems44,46, and/orinert units48 can be combined in any arrangement in astring20. In some embodiments, one or more of the connectors do not comprise a detonation control module.

FIG. 8F shows a string of several adjacent single-unit HE systems50, each arranged with the detonator at the same end of the system. In this arrangement, each connector controls the detonator to its left.FIG. 8G shows a string of double-unit HE systems44 connected directly together. In this arrangement, each double-unit HE system44 is coupled directly to the next double-unit HE system without any intermediate connectors. In this matter, some of the connectors in a string can be eliminated. Connectors can also be removed or unnecessary wheninert units48 are included in the string.

In some embodiments, a system for enhancing permeability includes one or more HE systems, such as one to twelve or more HE systems and one or more PP systems, such as one to twelve or more PP systems, which are arranged in a rack/column along astring20. In some examples, each HE system is separated from another HE system by one or more PP systems, such as one to eight or more PP systems. In some embodiments, thestring20 can comprise a generally cylindrical rack/column of about 20 feet to about 50 feet in length, such as about 30 feet to about 50 feet. In some examples, each HE system and each PP system is about 2 feet to about 12 feet in length, such as about 3 feet to about 10 feet in length.

Each of theunits20 can comprise a casing, such as a generallycylindrical casing22 as shown in cross-section inFIG. 6. In some examples, the casing is designed to contain the HE, PP, or inert material. The casing can also separate the contained material from the fluid38 that fills thebore16 outside of the casing. In some examples, the casing completely surrounds the contained material to separate it completely from the fluid filling the bore. In some examples, the casing only partial surrounds the contained material thereby only partially separating it from the material filling the bore.

In some embodiments, the PP units can be ignited prior to the HE units. This can cause the PP ignited product (e.g., a gas and/or liquid) to quickly expand and fill any regions of the bore outside of the HE units, including regions of the bore not filled with other fluid. The quickly expanding PP product can further force other fluids in the bore further into smaller and more distant cracks and spaces between the solid materials of the target zone before the HE units detonate. Filling the bore with the PP product and/or other fluid prior to detonation of the HE units in this manner can mitigate the crushing of the rock directly adjacent to the bore caused by the HE explosion because the fluid between the HE units and the bore walls acts to transfer the energy of the explosion further radially away from the centerline of the bore without as violent of a shock to the immediately adjacent bore walls. Avoiding the crushing of the bore wall material is desirable for it reduces the production of sand and other fine particulates, which can clog permeability paths and are therefore counterproductive to liberating energy resources from regions of the target zone distant from the bore. Moreover, reducing the near-bore crushing and pulverization reduces the energy lost in these processes, allowing more energy to flow radially outward further with the shock wave and contribute to fracture in an extended region.

The dimensions (size and shape) and arrangement of the HE and PP units and connectors can vary according to the type of geologic formation, bore size, desired rubblization zone, and other factors related to the intended use. In some examples, the case(s)22 can be about ¼ inches to about 2 inches thick, such as ¼, ½, ¾, 1, 1¼, 1½, 1¾, and 2 inches thick. In some examples, the material between thecase22 and thebore wall16 can be about 0 inches to about 6 inches thick. Thecases22 can contact the bore walls in some locations, while leaving a larger gap on the opposite side of the case from the contact with the bore. The thickness of the material in the bore between the cases and the bore wall can therefore vary considerably along the axial length of thestring20. In some examples, the HE (such as a non-ideal HE) is about 4 inches to about 12 inches in diameter, within acase22. For example, a disclosed system includes a 6½ inch diameter of HE, ½ inch metal case (such aluminum case) and 1¼ inch average thickness of material between the case and the bore wall (such as a 1¼ inch thick brine and/or PP layer) for use in a 10 inch bore. Such a system can be used to generate a rubblization zone to a radius of an at least three times improvement over a continuous charge of equal yield, such as a six times improvement. For example, the explosive charges can be detonated and/or the combustion of each propellant charge initiated to fracture the section of the underground geologic formation in a first fracture zone adjacent to and surrounding the section of the bore hole and extending into the underground geologic formation to a first depth of penetration away from the section of the bore hole and plural second fracture zones spaced apart from one another and extending into the underground geologic formation to a second depth of penetration away from the section of the bore hole greater than the first depth of penetration, wherein the second fracture zones are in the form of respective spaced apart disc-like fracture zones extending radially outwardly from the bore hole and/or the second depth of penetration averages at least three times, such as at least six times, the average first depth of penetration. In some examples, a disclosed system includes a 9½ inch diameter of HE (such as a non-ideal HE), ¼ inch metal case (such aluminum case) and 1 inch average thickness of material between the case and the bore wall (such as a 1 inch thick brine and/or PP layer) for use in a 12 inch borehole. It is contemplated that the dimensions of the system can vary depending upon the size of the bore.

In some embodiments, the system for enhancing permeability further includes engineered keyed coupling mechanisms between HE and PP units and the connectors. Such coupling mechanisms can include mechanical coupling mechanisms, high-voltage electrical coupling mechanisms, communications coupling mechanisms, high voltage detonator or initiation systems (planes), and/or monitoring systems. In some examples, independently timed high-precision detonation and initiation planes for each HE and PP section, respectively, can be included. Such planes can include customized programmable logic for performing tasks specific to the system operated by the plane, including safety and security components, and each plane can include carefully keyed coupling mechanisms for mechanical coupling, including coupling detonators/initiators into the HE/PP, high-voltage coupling, and communications coupling.

In some examples, cast-cured HE and PP section designs, including high-voltage systems, communication systems, detonator or initiation systems, and monitoring systems, are such that they can be manufactured, such as at an HE Production Service Provider Company, and then safely stored and/or “just in time” shipped to a particular firing site for rapid assembly into ruggedized HE-PP columns, testing and monitoring, and deployment into a bore. Specific formulations utilized, and the geometrical and material configurations in which the HE and PP systems are deployed, can be central for producing a desired rubblization effects in situ within each particular geologic formation. In some examples, these optimized geometric and material configurations can be produced via specifically calibrated numerical simulation capabilities that can include many implementations of models into the commercial code ABAQUS. In further examples, any of the disclosed systems can be developed/up-dated by use of a High Fidelity Mobile Detonation Physics Laboratory (HFMDPL), as described in detail herein (see, for example, Section IX).

IV. Exemplary High Explosive and Propellant Units and Systems

FIG. 9 shows anexemplary unit100, which can comprise a HE unit, a PP unit, or an inert unit. Theunit100 comprises a generally cylindrical,tubular case102 having at least one interior chamber for containing amaterial150, such as HE material, PP material, brine, or other material. Theunit100 comprises a firstaxial end portion104 and a second oppositeaxial end portion106. Eachaxial end portion104,106 is configured to be coupled to a connector, to another HE, PP or inert unit, or other portions of a bore insertion string. Thecasing102 can comprise one or more metals, metal alloys, ceramics, and/or other materials or combinations thereof. In some embodiments, thecasing102 comprises aluminum or an aluminum alloy.

Theaxial end portions104,106 can comprise mechanical coupling mechanisms for supporting the weight of the units along a string. The mechanical coupling mechanisms can comprise external threadedportions108,110,plate attachment portions112,114, and/or any other suitable coupling mechanisms. For example,FIGS. 14A-14D show representative suitable mechanical coupling mechanisms. Theaxial end portions104,106 can further comprise electrical couplings, such as one ormore wires116, that electrically couple the unit to the adjacent connectors, other units in the string, and/or to control systems outside of the bore. Thewires116 can pass axially through the length of theunit100 and extend from either end for coupling to adjacent components.

As shown in detail inFIG. 10, theunit100 can further comprise afirst end cap118 coupled to theaxial end portion106 of thecase102 and/or asecond end cap120 coupled to the oppositeaxial end portion108 of thecase102. The end caps118,120 can comprise an annular body having a perimeter portion that is or can be coupled to the axial end of thecase102. The end caps118,120 can be fixed to thecasing102, such as be welding, adhesive, fasteners, threading, or other means. The end caps118,120 can comprise any material, such as one or more metals, metal alloys, ceramics, polymeric materials, etc. In embodiments with the end caps welded to the casing, the full penetration welds can be used in order to preclude thing metal-to-metal gaps in which migration of chemical components could become sensitive to undesired ignition. In embodiments having polymeric end caps, thin contact gaps can exist between the caps and the casing with less or no risk of undesired ignition. Polymeric end caps can be secured to the casing via threading and/or a polymeric retaining ring. Furthermore, a sealing member, such as an O-ring, can be positioned between the end cap and the casing to prevent leakage ormaterial150 out of the unit. In other embodiments, metallic end caps can be used with annular polymeric material positioned between the end caps and the casing to preclude metal-to-metal gaps.

The outer diameter of the units and/or connectors can be at least partially covered with or treated with a friction-reducing layer and/or surface treatment. This treatment layer or treatment can comprise at least one of the following: solid lubricants, such as graphite, PTFE containing materials, MoS2, or WS2; liquid lubricants, such as petroleum or synthetic analogs, grease; or aqueous based lubricants. Surface treatments can include attached material layers, such as WS2 (trade name Dicronite®); MoS2, metals having high lubricity, such as tin (Sn), polymer coatings exhibiting high lubricity such as fluoropolymers, polyethylene, PBT, etc.; physically deposited, electroplated, painting, powder coating; or other materials.

Wires116 (such as for controlling, powering and triggering the detonation of the energetic material) pass through or at least up to eachunit100. Any number ofwires116 can be included, such as one, two, four, or more. At least some of thewires116 can pass through at least one of the end caps118,120 on the ends of each unit, as shown inFIG. 10. The penetrations in the end caps and the penetratingwires116 can be free of thin metal-to-metal gaps in which migration of chemical components could become sensitive to undesired ignition.

In some embodiments, the end caps118,120 can comprise one ormore penetration glands122 designed to obviate undesired ignition by eliminating or reducing thin metal-to-metal gaps and preventing leakage ofmaterial150 out of theunit100. Thepenetration glands122 can be configured to provide thin gaps between polymeric and metal surface penetration holes. The compliance of polymer-to-metal or polymer-to-polymer thin gaps can prevent sufficient compression and friction for sensitive chemical components to ignite.

As shown in more detail inFIG. 11, eachpenetration gland122 can receive awire116 with apolymer jacket124 passing through ahole126 in theend cap118,120. Thewire116 can be sealed with a compliant seal, such as an O-ring128. The seal is compressed in place by apolymeric fastener130, which is secured to the end cap, such as via threads, and tightened to compress the seal. Thefastener130 can comprise a hole through its axis through which thewire116 passes.

In other embodiments, a penetration gland can be comprised of a threaded hole with a shoulder, a gland screw with a coaxial through-hole, said screw having a shoulder which compresses a seal (such as an o-ring) in order to seal the cable passing through it. Coaxial cable can allow two conductors to be passed through each seal gland with an effective seal between the inside of the unit and the outside of the unit.

Theunit100 can further comprise at least onedetonator holder140 and at least onedetonator142 and at least one axial end of the unit, as shown inFIG. 10. The term detonator includes any device used to detonate or ignite thematerial150 within the unit, or initiate or cause thematerial150 to detonate or ignite or explode, or to initiate or cause a chemical reaction or expansion of thematerial150. In an HE filled unit, the unit can comprise asingle detonator142 at one end of the unit, such as at theend portion106, with no second detonator at the opposite end of the unit. In a PP filled unit, the unit can comprise adetonator142 at both axial end portions of the unit, each being generally similar in structure and function.

Thedetonator holder140, as shown inFIG. 10, for either a HE unit or a PP unit, can comprise a cup-shaped structure positioned within a central opening in theend cap118. Theholder140 can be secured to and sealed to theend cap118, such as viathreads144 and an O-ring146. Theholder140 extends axially through theend cap118 into the chamber within thecasing102 such that theholder140 can be in contact with thematerial150. Theholder140 can comprise acentral opening148 at a location recessed within the casing and thedetonator142 can be secured within theopening148. Aninternal end152 of the detonator can be held in contact with the material150 with a contact urging mechanism to ensure the detonator does not lose direct contact with thematerial150 and to ensure reliable ignition of thematerial150. The urging mechanism can comprise a spring element, adhesive, fastener, or other suitable mechanism.

Thedetonator142 can further comprise anelectrical contact portion154 positioned within the recess of theholder140. Theelectrical contact portion154 can be positioned to be not extend axially beyond the axial extend of the rim of theholder140 to prevent or reduce unintended contact with thedetonator142. Theelectrical contact portion154 can be electrically coupled to a detonation control module in an adjacent connector via wires.

In some embodiments, a unit can comprise right-handed threads on one axial end portion of the casing and left-handed threads on the other axial end portion of the casing. As shown inFIG. 12, the oppositely threaded ends of each unit can facilitate coupling two units together with an intermediate connector. In the example shown inFIGS. 12-14A, asystem200 can be formed by coupling an exemplaryfirst unit202 and an exemplarysecond unit204 together with anexemplary connector206.FIGS. 13 and 14A show cross-sectional views taken along a longitudinal axis of thesystem200 in an assembled state. The first andsecond units202,204 can be identical to or similar to the illustratedunit100 shown inFIGS. 9-11, or can comprise alternative variations of units. For example, theunits202,204 can comprise HE units that are similar or identical, but oriented in opposite axial directions such that their lone detonators are both facing theconnector206.

Theconnector206 can comprise a tubularouter body208 having firstinternal threads210 at one end and second internal threads at the second opposite end, as shown inFIG. 12. Mechanical coupling of theunits202,204, andconnector206 can be accomplished by rotatingconnector206 relative to theunits202,204 (such as with theunits202,204 stationary), such thatinternal threads210,212 thread ontoexternal threads214,216 of theunits202,204, respectively. The rotation of theconnector206 can act like a turnbuckle to draw theadjacent units202,204 together. Thethreads210,212,214,216 can comprise buttress threads for axial strength.

After the adjacent pair ofunits202,204 are drawn together, lockingplates218,220 can be attached to each unit end portion and engageslots222,224, respectively in each end of the connectorouter body208 to prevent unintentional unscrewing of the joint.Lock plates218,220 are attached to each unit by fastening means (e.g., screws240,242 and screwholes244,246 in the unit case). The fastening means preferably do not pass through the case wall to avoid allowing the containedmaterial250 to escape and so that the system remains sealed. Thelock plates218,220 prevent theconnector206 from unscrewing from theunits202,204 to insure that the assembly stays intact.

The described threaded couplings between the units and the connectors can provide axial constraint of sections of a tool string to each other, and can also provide compliance in off-axis bending due to thread clearances. This can allow the tool string to bend slightly off-axis at each threaded joint such that it can be inserted into a bore which has a non-straight contour. One advantage of the described locking plate configuration is to eliminate the need for torquing the coupling threads to a specified tightness during assembly in the field. In practice, the connector shoulders (226,228 inFIG. 12) need not be tightened to intimately abut the unit shoulders (230,232 inFIG. 12) axially, but some amount of clearance can be left between the connector and unit shoulders to assure torque is not providing any, or only minimal, axial pre-stress on the system. This small clearance can also enhance the off-axis bending compliance of the tool string in conjunction with the thread clearances.

Theconnector206 can further comprise adetonation control module260 contained within theouter body208. Thedetonation control module260 can be configured to be freely rotatable relative to theouter body208 about the central axis of the connector, such as via rotational bearings between the outer body and the detonation control module. Thedetonation control module260 can comprise astructural portion262 to which theelectrical portions264 are mounted. Theelectrical portions264 of thedetonation control module260 are described in more detail below.

During assembly of theconnector260 to theunits202,204, thedetonation control module206 can be held stationary relative to theunits202,204 while theouter body208 is rotated to perform mechanical coupling. To hold thedetonation control module260 stationary relative to theunits202,204, one or both of the units can comprise one or more projections, such as pins266 (seeFIG. 13), that project axially away from the respective unit, such as from the end caps, and into a receiving aperture orapertures268 in thestructural portion262 of thedetonation control module260. The pin(s)266 can keep thedetonation control module260 stationary relative to theunits202,204 such that electrical connections therebetween do not get twisted and/or damaged. In some embodiments, only one of theunits202,204 comprises an axial projection coupled to thestructural portion262 of thedetonation control module260 to keep to stationary relative to the units as the outer casing is rotated.

Theunits202,204 can comprise similar structure to that described in relation to theexemplary unit100 shown inFIGS. 9-11. As shown inFIGS. 13 and 14A, theunit202 compriseselectrical wires270 extending through the material250 in the unit and throughglands272 in anend cap274. Theunit202 further comprises adetonator holder276 extending through theend cap272 and adetonator278 extending through theholder276.Unit204 also comprises similar features.Electrical connections280 of the detonator and282 of thewires270 can be electrically coupled to thedetonation control module260, as describe below, prior to threading the connector to the twounits202,204.

FIGS. 14B-14D shows cross-sectional views of alternative mechanical coupling mechanisms for attaching the units to the connectors. In each ofFIGS. 14B-14D, some portions of the devices are omitted. For example, the detonation control module, detonator, wiring, and fill materials are not shown. The detonator holder and/or end caps of the units may also be omitted from these figures.

FIG. 14B shows anexemplary assembly300 comprising a unit302 (such as an HE or PP unit) and aconnector304. Theunit302 comprises a casing and/or end cap that includes a radially recessedportion306 and anaxial end portion308. Theconnector304 comprises anaxial extension310 positioned around the radially recessedportion306 and aninner flange312 positioned adjacent to theaxial end portion308. One or more fasteners314 (e.g., screws) are inserted through theconnector304 at an angle between axial and radial. Thefasteners314 can be countersunk in the connector to preserve a smooth outer radial surface of the assembly. Thefasteners314 can extend through theinner flange312 of the connector and through theaxial end portion308 of the unit, as shown, to mechanically secure the unit and the connector together. A sealingmember316, such as an O-ring, can be positioned between theinner flange312 and theaxial end portion308, or elsewhere in the connector-unit joint, to seal the joint and prevent material contained within the assembly from escaping and prevent material from entering the assembly.

FIG. 14C shows anotherexemplary assembly320 comprising a unit322 (such as an HE or PP unit), aconnector324, and one ormore locking plates326. Theunit322 comprises a casing and/or end cap that includes a radially recessedportion328 and anaxial end portion330. Theconnector324 comprises anaxial extension332 positioned adjacent to the radially recessedportion328 and aninner flange334 positioned adjacent to theaxial end portion330. A sealingmember336, such as an O-ring, can be positioned between theinner flange334 and theaxial end portion330, or elsewhere in the connector-unit joint, to seal the joint and prevent material contained within the assembly from escaping and prevent material from entering the assembly. The locking plate(s)326 comprise afirst ledge338 that extends radially inwardly into a groove inunit322, and asecond ledge340 that extends radially inwardly into a groove in theconnector324. The first andsecond ledges338,340 prevent theunit322 and theconnector324 from separating axially apart from each other, locking them together. The plate(s)326 can be secured radially to the assembly with one ormore fasteners342, such as screws, that extend radially through theplate326 and into the connector324 (as shown) or into theunit322.

FIG. 14D shows yet anotherexemplary assembly350 comprising a unit352 (such as an HE or PP unit), aconnector354, and one ormore locking plates356. Theunit352 comprises a casing and/or end cap that includes a radially recessedportion358 and anaxial end portion360. Theconnector354 comprises anaxial extension362 positioned adjacent to the radially recessedportion358 and aninner flange364 positioned adjacent to theaxial end portion360. A sealingmember366, such as an O-ring, can be positioned between theinner flange364 and theaxial end portion360, or elsewhere in the connector-unit joint, to seal the joint and prevent material contained within the assembly from escaping and prevent material from entering the assembly. The locking plate(s)356 comprise afirst ledge368 that extends radially inwardly into a groove inunit352, and asecond ledge370 that extends radially inwardly into a groove in theconnector354. The first andsecond ledges368,370 prevent theunit352 and theconnector354 from separating axially apart from each other, locking them together. The plate(s)376 can be secured radially to the assembly with one or more resilient bands or rings372, such as an elastomeric band, that extends circumferentially around theassembly350 to hold the plate(s) to theconnector354 and to theunit352. The band(s)372 can be positioned in an annular groove to maintain a flush outer surface of theassembly350.

The assemblies shown inFIGS. 14A-14D are just examples of the many different possible mechanical couplings that can be used in the herein described systems and assemblies. It can be desirable that the mechanical couplings allow for some degree of off-axis pivoting between the unit and the connector to accommodate non-straight bore, and/or that the mechanical coupling imparts minimal or no axial pre-stress on the string, while providing sufficient axial strength to hold the string axially together under its own weight when in a bore and with additional axial forces imparted on the string due to friction, etc.

PP units and systems can be structurally similar to HE units and systems, and both can be described in some embodiments by exemplary structures shown inFIGS. 9-14. However, while HE units can comprise only a single detonator, in some PP units and PP systems, the PP unit can comprise two detonators/ignition systems, one positioned at each end of the unit. The PP ignition systems can be configured to simultaneously ignite the PP material from both ends of the unit. The two opposed PP ignition systems can comprise, for example, ceramic jet ignition systems. The PP ignitions systems can rapidly ignite the PP material along the axial length of the PP unit to help ignite the PP material in a more instantaneous matter, rather than having one end of the unit ignite first then wait for the reaction to travel down the length of the PP unit to the opposite end. Rapid ignition of the PP material can be desirable such that the PP ignition product material can quickly expand and fill the bore prior to the ignition of the HE material.

V. Exemplary Systems with Initially Segregated Energetic Material Components

In some exemplary systems, the explosive energetic material is initially segregated into separate components, such as a fuel and an oxidizer. Before the separate components are combined, the materials can be more chemically stable and safer, preventing or reducing the risk of premature explosions. Near to the time of desired detonation, the components can be combined such that are ready for detonation. This can occur after the system is inserted into a wellbore at a desired location, for example.

In some embodiments, explosive units are initially preloaded with a first component of an explosive mixture before the units are assembled and inserted into a wellbore. Then, a second component of the explosive mixture can be conducted down the wellbore into the explosive units such that it combines with the first component within each unit.

The first component can comprise a permeable solid material, such as a powder or sponge-like material, a liquid, or a mixture of solid and liquid material. For example, the first component can comprise an oxidizing agent, or oxidizer. Exemplary oxidizers can be rich in oxygen atoms, for example, or other atoms that tend to gain electrons in an explosion. In other embodiments, the first material can comprise a permeable solid and/or liquid fuel component.

The second component can comprise a liquid or liquid mixture that can flow through conduits into the explosive units and mix with the first component. For example, the second component can comprise a liquid fuel or liquid oxidizer.

FIG. 27 shows a cross-sectional view of an exemplaryexplosive unit900 that comprises acasing902 defining aninternal chamber904 containing a first component of an explosive mixture. Thecasing902 includeslongitudinal end portions906 and aninlet tube908 extends through at least one of the end portions into theinternal chamber904. Theexplosive unit900 can further comprise one ormore initiator assemblies910 including adetonator912 that extend through theend portions906 into thechamber904. In the illustrated example, the first component preloaded in thechamber904 comprises a permeable solid oxidizer. Prior to detonation, a second component of the explosive mixture can be conducted into thechamber904 to mix with the first component and form the explosive mixture. The second component is a liquid fuel in this example.

FIG. 28 is a diagram of anexemplary system920 comprising pluralexplosive units922a,922b,922ccoupled end to end and aninlet conduit924 extending through the explosive units. The explosive units can be coupled together withmechanical couplers928 and theinlet conduit924 can comprise discrete sections that are joined withconduit couplers930 within themechanical couplers928 between the explosive units. Theinlet conduit924 can thus form a fluid pathway from a proximal source through the proximalexplosive units922a,922band into the distalexplosive unit922c. Theinlet conduit924 can further comprise fluid exits926a,926b,926cwithin the internal chambers of each explosive unit922 such that a fluid component of an explosive mixture can be conducted into the internal chambers to mix with the preloaded component of the explosive mixture. The fluid exits926 can be configured to allow predetermined amounts of the fluid into each respective internal chamber.

In the example ofFIG. 28, no venting of the internal chambers is provided. Thus, the system can rely on relatively low pressure created within the internal chambers and/or relative high pressure applied to the fluid inlet conduit to cause the fluid to enter the chambers. For example, the internal chambers of the units can have a partial vacuum applied prior to conducting the liquid into them, such that the liquid is sucked into the units.FIG. 29 shows anexemplary system940 wherein aninlet conduit944 is coupled to aliquid supply source950 and avacuum pump952 via aselector valve954. In some methods, the vacuum pump can first be applied to generate a reduced pressure within the internal chambers of theexplosive units942a,942b,942c. Then the liquid can be conducted down theinlet conduit944 into the internal chambers via liquid exits946a,946b,946cand viaconduit couplers948 between the explosive units. The reduce pressure caused by thevacuum pump952 can facilitate the flow of the liquid into the internal chambers and can facilitate the mixing/permeating of the liquid with the preloaded component of the explosive mixture. Theliquid supply source950 can further be pressurized, such as with a pump and/or via gravity, to further encourage the flow of liquid into the internal chambers of the units942.

In other embodiments, the internal chambers of the explosive units can be vented to facilitate the flow of gas and liquid into and/or through the internal chambers and to facilitate the venting of gas from the internal chambers.

For example,FIG. 30 shows anexemplary system960 that comprisesexplosive units962a,962b,962ccoupled withconnectors964. The system includes aninlet conduit966 that extends through theproximal units962a,962band has a singleliquid exit968 within thedistal unit962c. Theinlet conduit966 can includeconduit couplers976 between the explosive units. As liquid is conducted into thedistal unit962c, gasses are vented from thedistal unit962cthough afirst outlet conduit970 into the nextexplosive unit962b. The vented gas is then conducted through asecond outlet conduit972 into thenext unit962a(and optionally any number of additional intermediate units and conduit couplers) before exiting the system via aproximal vent conduit974. Theoutlet conduits970,972, etc., can compriseconduit couplers978 between the explosive units.

Liquid entering thedistal unit962cfrom theinlet conduit966 mixes or permeates with a preloaded explosive component, and as the distal unit fills with the liquid, the liquid can continue flowing through thefirst outlet conduit970 into thenext unit962b, then through thesecond outlet conduit972 into thenext unit962a, etc., until the explosive units are all filled with liquid. Valves can be provided at various points along the inlet conduit and the outlet conduits to control the venting of gas and inflow of liquid. For example, a valve can be positioned at the outlet from the most proximal explosive unit such that after gas is vented, the liquid being conducted into the units can be blocked from exiting. Gravitational hydrostatic pressure can be sufficient to cause the liquid to descend into and fill the explosive units and cause the less dense gas to ascend from the units and vent out of the system. In other embodiments, pumps can be used to encourage the flow and/or valves can be used to control the flow.

FIG. 31 is a diagram of anotherexemplary system980 similar to thesystem960 ofFIG. 30, comprising aliquid supply source986, anoptional pump988, and avalve990 coupled to theinlet conduit984 proximal toexplosive units982a,982b,982c. Thepump988 and/or gravity can add pressure to the liquid entering the units. The liquid exits theinlet conduit984 through aliquid exit992 into thedistal unit982c, then travels proximally through theoutlet conduits993,994, etc., into the moreproximal units982a,982c, etc. Gas exiting the explosive units is vented throughvent995, optionally into avent catch tank996 and out through acatch tank exit998.

In the embodiments ofFIGS. 27-31, the inlet and outlet conduits can comprise flexible conduits to allow from flexing of the downhole string as it is inserted into various shaped wellbores.

In embodiments wherein the explosive units are preloaded with a permeable, powders or sponge-like first component, the voids within the material can be configured and size to allow for sufficient flow of the liquid through the material to give proper stoichiometry in the mixture and/or to allow the liquid to travel through outlet conduits into more proximal units.

VI. Exemplary Detonation Control Module and Electrical Systems

FIG. 15 is a block diagram illustrating an exemplarydetonation control module700.Detonation control module700 is activated bytrigger input signal701 and outputs apower pulse702 that triggers a detonator. In some embodiments,output power pulse702 triggers a plurality of detonators.Trigger input signal701 can be a common trigger signal that is provided to a plurality of detonation control modules to trigger a plurality of detonators substantially simultaneously. Detonators may detonate explosives, propellants, or other substances.

Detonation control module700 includestiming module703.Timing module703 provides a signal at a controlled time that activates a light-producingdiode704. Light-producingdiode704, which in some embodiments is a laser diode, illuminates optically triggereddiode705 in optically triggereddiode module706, causing optically triggereddiode705 to conduct. In some embodiments, optically triggereddiode705 enters avalanche breakdown mode when activated, allowing large amounts of current flow. When optically triggereddiode705 conducts, high-voltage capacitor707 in high-voltage module708 releases stored energy in the form ofoutput power pulse702. In some embodiments, a plurality of high-voltage capacitors are used to store the energy needed foroutput power pulse702.

FIG. 16A illustrates exemplarydetonation control module709.Detonation control module709 includestiming module710, optically triggereddiode module711, and high-voltage module712.Connectors713 and714connect timing module710 with various input signals such as input voltages, ground, trigger input signal(s), and others. Atiming circuit715 includes a number ofcircuit components716. Exemplary circuit components include resistors, capacitors, transistors, integrated circuits (such as a 555 or 556 timer), and diodes.

Timing module710 also includes light-producingdiode717.Timing circuit715 controls activation of light-producingdiode717. In some embodiments, light-producingdiode717 is a laser diode. Light-producingdiode717 is positioned to illuminate and activate optically triggereddiode718 on optically triggereddiode module711. Optically triggereddiode718 is coupled between a high-voltage capacitor719 and a detonator (not shown).

As shown inFIG. 16A,timing module710 is mechanically connected to high-voltage module712 viaconnectors720 and721.Optical diode module711 is both mechanically and electrically connected to high-voltage module712 viaconnectors722 and mechanically connected viaconnector723.

FIG. 16B illustrates optically triggereddiode module711. When optically triggereddiode718 is activated, a conductive path is formed between conductingelement724 and conductingelement725. The conductive path connects high-voltage capacitor719 with a connector (shown inFIG. 17) to a detonator (not shown) viaelectrical connectors722.

FIG. 16C illustrates high-voltage module712.Connectors726 and727 connect high-voltage capacitor719 to two detonators, “Det A” and “Det B.” In some embodiments, each ofconnectors726 and727 connect high-voltage capacitor719 to two detonators (a total of four). In other embodiments,detonation control module709 controls a single detonator. In still other embodiments,detonation control module709 controls three or more detonators. High-voltage capacitor719 provides an output power pulse to at least one detonator (not shown) viaconnectors726 and727.Connectors728 and729 provide a high-voltage supply and high-voltage ground used to charge high-voltage capacitor719. High-voltage module712 also includes ableed resistor730 andpassive diode731 that together allow charge to safely drain from high-voltage capacitor719 if the high-voltage supply and high-voltage ground are disconnected fromconnectors728 and/or729.

FIG. 17 is a schematic detailing an exemplary detonationcontrol module circuit732 that implements a detonation control module such asdetonation control module709 shown inFIGS. 16A-16C. Detonationcontrol module circuit732 includes atiming circuit733, an optically triggereddiode734, and high-voltage circuit735.Timing circuit733 includes atransistor736.Trigger input signal737 is coupled to the gate oftransistor736 throughvoltage divider738. InFIG. 17,transistor736 is a field-effect transistor (FET). Specifically,transistor736 is a metal oxide semiconductor FET, although other types of FETs may also be used. FETs, including MOSFETs, have a parasitic capacitance that provides some immunity to noise and also require a higher gate voltage level to activate than other transistor types. For example, a bipolar junction transistor (BJT) typically activates with a base-emitter voltage of 0.7 V (analogous totransistor736 having a gate voltage of 0.7 V). FETs, however, activate at a higher voltage level, for example with a gate voltage of approximately 4 V. A higher gate voltage (activation voltage) also provides some immunity to noise. For example, a 2V stray signal that might trigger a BJT would likely not trigger a FET. Other transistor types that reduce the likelihood of activation by stray signals may also be used. The use of the term “transistor” is meant to encompass all transistor types and does not refer to a specific type of transistor.

Zener diode739 protectstransistor736 from high-voltage spikes. Many circuit components, includingtransistor736, have maximum voltage levels that can be withstood before damaging the component.Zener diode739 begins to conduct at a particular voltage level, depending upon the diode.Zener diode739 is selected to conduct at a voltage level thattransistor736 can tolerate to prevent destructive voltage levels from reachingtransistor736. This can be referred to as “clamping.” For example, iftransistor736 can withstand approximately 24 V,zener diode739 can be selected to conduct at 12 V.

A “high”trigger input signal737 turns ontransistor736, causing current to flow fromsupply voltage740 throughdiode741 andresistor742. A group ofcapacitors743 are charged bysupply voltage740.Diode741 andcapacitors743 act as a temporary supply voltage ifsupply voltage740 is removed. Whensupply voltage740 is connected,capacitors743 charge. Whensupply voltage740 is disconnected,diode741 prevents charge from flowing back towardresistor742 and instead allows the charge stored incapacitors743 to be provided to other components.Capacitors743 can have a range of values. In one embodiment,capacitors743 include three 25 μF capacitors, a 1 μF capacitor, and a 0.1 μF capacitor. Having capacitors with different values allows current to be drawn fromcapacitors743 at different speeds to meet the requirements of other components.

There are a variety of circumstances in which supplyvoltage740 can become disconnected but where retaining supply voltage is still desirable. For example,detonation control module732 can be part of a system in which propellants are detonated prior to explosives being detonated. In such a situation, the timing circuitry that controls detonators connected to the explosives may need to continue to operate even if the power supply wires become either short circuited or open circuited as a result of a previous propellant explosion. The temporary supply voltage provided bydiode741 andcapacitors743 allows components that would normally have been powered bysupply voltage740 to continue to operate. The length of time the circuit can continue to operate depends upon the amount of charge stored incapacitors743. In one embodiment,capacitors743 are selected to provide at least 100 to 150 microseconds of temporary supply voltage. Another situation in which supplyvoltage740 can become disconnected is if explosions are staggered by a time period. In some embodiments,supply voltage740 is 6V DC andresistor742 is 3.3 kΩ. The values and number ofcapacitors743 can be adjusted dependent upon requirements.

Timing circuit733 also includes a dual timer integrated circuit (IC)744.Dual timer IC744 is shown inFIG. 17 as a “556” dual timer IC (e.g., LM556). Other embodiments use single timer ICs (e.g. “555”), quad timer ICs (e.g. “558”), or other ICs or components arranged to perform timing functions. The first timer indual timer IC744 provides a firing delay. The firing delay is accomplished by providing a first timer output745 (IC pin5) to a second timer input746 (IC pin8). The second timer acts as a pulse-shaping timer that provides a waveform pulse as a second timer output747 (IC pin9). Aftervoltage divider748, the waveform pulse is provided to aMOSFET driver input749 to drive aMOSFET driver IC750.MOSFET driver IC750 can be, for example, a MIC44F18 IC.

Timer ICs such asdual timer IC744, as well as the selection of components such asresistors751,752,753,754, and755 andcapacitors756,757,758, and759 to operatedual timer IC744, are known in the art and are not discussed in detail in this application. The component values selected depend at least in part upon the desired delays. In one embodiment, the following values are used:resistors751,752, and755=100 kΩ; andcapacitors756 and759=0.01 μF. Other components and component values may also be used to implementdual timer IC744.

MOSFET driver IC750 is powered bysupply voltage760 throughdiode761 andresistor762. In some embodiments,supply voltage760 is 6V DC andresistor762 is 3.3 kΩ.Supply voltage760 can be the same supply voltage assupply voltage740 that powersdual timer IC744. A group ofcapacitors763 are charged bysupply voltage760.Diode761 andcapacitors763 act to provide a temporary supply voltage whensupply voltage760 is disconnected or shorted. As discussed above,diode761 is forward biased betweensupply voltage760 and the power input pin of MOSFET driver IC750 (pin2).Capacitors763 are connected in parallel between the power input pin and ground.Capacitors763 can have a range of values.

MOSFET driver output764 activates adriver transistor765. In some embodiments,driver transistor765 is a FET.MOSFET driver IC750 provides an output that is appropriate for drivingtransistor765, whereassecond timer output747 is not designed to drive capacitive loads such as the parasitic capacitance of transistor765 (whentransistor765 is a FET).

Resistor766 andzener diode767 clamp the input todriver transistor765 to prevent voltage spikes fromdamaging transistor765. Whendriver transistor765 is activated, current flows fromsupply voltage768, throughdiode790 andresistor769 and activates a light-producingdiode770. In some embodiments,driver transistor765 is omitted andMOSFET driver output764 activates light-producingdiode770 directly.

In some embodiments, light-producingdiode770 is a pulsed laser diode such as PLD 905D1S03S. In some embodiments,supply voltage768 is 6V DC andresistor769 is 1 kΩ.Supply voltage768 can be the same supply voltage assupply voltages740 and760 that powerdual timer IC744 andMOSFET driver IC750, respectively. A group ofcapacitors771 are charged bysupply voltage768.Diode790 andcapacitors771 act to provide a temporary supply voltage whensupply voltage768 is removed (see discussion above regardingdiode741 and capacitors743).Capacitors771 can have a range of values.

When activated, light-producingdiode770 produces a beam of light. Light-producingdiode770 is positioned to illuminate and activate optically triggereddiode734. In some embodiments, optically triggereddiode734 is a PIN diode. Optically triggereddiode734 is reverse biased and enters avalanche breakdown mode when a sufficient flux of photons is received. In avalanche breakdown mode, a high-voltage, high-current pulse is conducted from high-voltage capacitor772 todetonator773, triggeringdetonator773. In some embodiments, additional detonators are also triggered by the high-voltage, high-current pulse.

High-voltage capacitor772 is charged by high-voltage supply774 throughdiode775 andresistor776. In one embodiment, high-voltage supply774 is about 2800 V DC. In other embodiments, high-voltage supply774 ranges between about 1000 and 3500 V DC. In some embodiments, a plurality of high-voltage capacitors are used to store the energy stored in high-voltage capacitor772.Diode775 prevents reverse current flow and allows high-voltage capacitor to still provide a power pulse todetonator773 even if high-voltage supply774 is disconnected (for example, due to other detonations of propellant or explosive). Bleed resistor777 allows high-voltage capacitor772 to drain safely if high-voltage supply774 is removed. In one embodiment,resistor776 is 10 kΩ, bleed resistor777 is 100 MΩ, and high-voltage capacitor772 is 0.2 μF. High-voltage capacitor772, bleed resistor777,resistor776, anddiode775 are part of high-voltage circuit735.

FIG. 18 illustrates amethod778 of controlling detonation. Inprocess block779, a laser diode is activated using at least one timing circuit. Inprocess block780, an optically triggered diode is illuminated with a beam produced by the activated laser diode. Inprocess block781, a power pulse is provided from a high-voltage capacitor to a detonator, the high-voltage capacitor coupled between the optically triggered diode and the detonator.

FIGS. 15-18 illustrate a detonation control module in which a light-producing diode activates an optically triggered diode to release a high-voltage pulse to trigger a detonator. Other ways of triggering a detonator are also possible. For example, a transformer can be used to magnetically couple a trigger input signal to activate a diode and allow a high-voltage capacitor to provide a high-voltage pulse to activate a detonator. Optocouplers, for example MOC3021, can also be used as a coupling mechanism.

A detonation system can include a plurality of detonation control modules spaced throughout the system to detonate different portions of explosives.

VII. Exemplary Methods of Use

The herein described systems are particularly suitable for use in fracturing an underground geologic formation where such fracturing is desired. One specific application is in fracturing rock along one or more sections of an underground bore hole to open up cracks or fractures in the rock to facilitate the collection of oil and gas trapped in the formation.

Thus, desirably a plurality of spaced apart explosive charges are positioned along a section of a bore hole about which rock is to be fractured. The explosive charges can be placed in containers such as tubes and plural tubes can be assembled together in an explosive assembly. Intermediate propellant charges can be placed between the explosive charges and between one or more assemblies of plural explosive charges to assist in the fracturing. The propellant charges can be placed in containers, such as tubes, and one or more assemblies of plural propellant charges can be positioned between the explosive charges or explosive charge assemblies. In addition, containers such as tubes of an inert material with a working liquid being a desirable example, can be placed intermediate to explosive charges or intermediate to explosive charge assemblies. This inert material can also be positioned intermediate to propellant charges and to such assemblies of propellant charges. The “working fluid” refers to a substantially non-compressible fluid such as water or brine, with saltwater being a specific example. The working fluid or liquid assists in delivering shockwave energy from propellant charges and explosive charges into the rock formation along the bore hole following initiation of combustion of the propellant charges and the explosion of the explosives.

In one specific approach, a string of explosive charge assemblies and propellant charge assemblies are arranged in end to end relationship along the section of a bore hole to be fractured. The number and spacing of the explosive charges and propellant charges, as well as intermediate inert material or working fluid containing tubes or containers, can be selected to enhance fracturing.

For example, a numerical/computational analysis approach using constituent models of the material forming the underground geologic formation adjacent to the bore hole section and of the explosive containing string can be used. These analysis approaches can use finite element modeling, finite difference methods modeling, or discrete element method modeling. In general, data is obtained on the underground geologic formation along the section of the bore hole to be fractured or along the entire bore hole. This data can be obtained any number of ways such as by analyzing core material obtained from the bore hole. This core material will indicate the location of layering as well as material transitions, such as from sandstone to shale. The bore hole logging and material tests on core samples from the bore hole, in the event they are performed, provide data on stratrigraphy and material properties of the geologic formation. X-ray and other mapping techniques can also be used to gather information concerning the underground geologic formation. In addition, extrapolation approaches can be used such as extrapolating from underground geologic formation information from bore holes drilled in a geologically similar (e.g., a nearby) geologic area.

Thus, using the finite element analysis method as a specific example, finite element modeling provides a predictive mechanism for studying highly complex, non-linear problems that involve solving, for example, mathematical equations such as partial differential equations. Existing computer programs are known for performing an analysis of geologic formations. One specific simulation approach can use a software program that is commercially available under the brand name ABAQUS, and more specifically, an available version of this code that implements a fully coupled Euler-Lagrange methodology.

This geologic data can be used to provide variables for populating material constitutive models within the finite element modeling code. The constitutive models are numerical representations of cause-and-effect for that particular material. That is, given a forcing function, say, pressure due to an explosive load, the constitutive model estimates the response of the material. For example, these models estimate the shear strain or cracking damage to the geologic material in response to applied pressure. There are a number of known constitutive models for geologic materials that can be used in finite element analysis to estimate the development of explosive-induced shock in the ground. These models can incorporate estimations of material damage and failure related directly to cracking and permeability. Similar constitutive models also exist for other materials such as an aluminum tube (if an explosive is enclosed in an aluminum tube) and working fluid such as brine.

In addition, equations of state (EOS) exist for explosive materials including for non-ideal explosives and propellants. In general, explosive EOS equations relate cause-and-effect of energy released by the explosive (and propellant if any) and the resulting volume expansion. When coupled to a geologic formation or medium, the expansion volume creates pressure that pushes into the medium and causes fracturing.

In view of the above, from the information obtained concerning the geologic material along the section of a bore hole to be fractured, a constitutive model of the material can be determined. One or more simulations of the response of this material model to an arrangement of explosive charges (and propellant charges if any, and working fluid containers, if any) can be determined. For example, a first of such simulations of the reaction of the material to explosive pressure from detonating explosive charges, pressure from one or more propellant charges, if any, and working fluids if any, can be performed. One or more additional simulations (for example plural additional simulations) with the explosive charges, propellant charges if any, and/or working fluids, if any, positioned at different locations or in different arrangements can then be performed. The simulations can also involve variations in propellants and explosives. The plural simulations of the reaction of the material to the various simulated explosive strings can then be evaluated. The simulation that results in desired fracturing, such as fracturing along a bore hole with spaced apart rubblization areas comprising radially extending discs, as shown inFIG. 21, can then be selected. The selected arrangement of explosive charges, propellant charges, if any, and working fluids, if any, can then be assembled and positioned along the section of the bore hole to be fractured. This assembly can then be detonated and the propellant charges, if any, initiated to produce the fractured geologic formation with desired rubblization zones. Thus, rubblization discs can be obtained at desired locations and extended radii beyond fracturing that occurs immediately near the bore hole.

The timing of detonation of explosives and initiation of combustion of various propellant charges can be independently controlled as described above in connection with an exemplary timing circuit. For example, the explosives and propellant initiation can occur simultaneously or the propellant charges being initiated prior to detonating the explosives. In addition, one or more explosive charges can be detonated prior to other explosive charges and one or more propellant charges can be initiated prior to other propellant charges or prior to the explosive charges, or at other desired time relationships. Thus, explosive charges can be independently timed for detonation or one or more groups of plural explosive charges can be detonated together. In addition, propellant charges can be independently timed for initiation or one or more groups of plural propellant charges can be initiated together. Desirably, initiation of the combustion propellant charges is designed to occur substantially along the entire length of, or along a majority of the length of, the propellant charge when elongated propellant charge, such as a tube, is used. With this approach, as the propellant charge burns, the resulting gases will extend radially outwardly from the propellant charges. For example, ceramic jet ejection initiators can be used for this purpose positioned at the respective ends of tubular propellant charges to eject hot ceramic material or other ignition material axially into the propellant charges. In one desirable approach, combustion of one or more propellant charges is initiated simultaneously at both ends of the charge or at a location adjacent to both ends of the charge. In addition, in one specific approach, assemblies comprising pairs of explosive charges are initiated from adjacent ends of explosive charges.

Desirably, the explosive charges are non-ideal explosive formulations such as previously described. In one specific desirable example, the charges release a total stored energy (e.g., chemically stored energy) equal to or greater than 12 kJ/cc and with greater than thirty percent of the energy released by the explosive being released in the following flow Taylor Wave of the detonated (chemically reacting) explosive charges.

In one approach, an assembly of alternating pairs of propellant containing tubes and explosive containing tubes, each tube being approximately three feet in length, was simulated. In the simulation, detonation of the explosives and simultaneous initiation of the propellant charges provided a simulated result of plural spaced apart rubblization discs extending radially outwardly beyond a fracture zone adjacent to and along the fractured section of the bore hole.

Desirably, the explosive charges are positioned in a spaced apart relationship to create a coalescing shock wave front extending radially outwardly from the bore hole at a location between the explosive charges to enhance to rock fracturing.

The system can be used without requiring the geologic modeling mentioned above. In addition, without modeling one can estimate the reaction of the material to an explosive assembly (which may or may not include propellant charges and working fluid containers) and adjust the explosive materials based on empirical observations although this would be less precise. Also, one can simply use strings of alternating paired explosive charge and paired propellant charge assemblies. In addition, the timing of detonation and propellant initiation can be empirically determined as well. For example, if the geologic material shows a transition between sandstone and shale, one can delay the sandstone formation detonation just slightly relative to the detonation of the explosive in the region of the shale to result in fracturing of the geologic formation along the interface between the sandstone and shale if desired.

Unique underground fractured geologic rock formations can be created using the methods disclosed herein. Thus, for example, the explosion and/or propellant gas created fracture structures (if propellants are used) can be created adjacent to a section of a previously drilled bore hole in the geologic rock formation or structure. The resulting fractured structure comprises a first zone of fractured material extending a first distance away from the location of the previously drilled bore hole. Typically this first zone extends a first distance from the bore hole and typically completely surrounds the previously existing bore hole (previously existing allows for the fact that the bore hole may collapse during the explosion). In addition, plural second zones of fractured material spaced apart from one another and extending radially outwardly from the previously existing bore hole are also created. The second fracture zones extend radially outwardly beyond the first fracture zone. Consequently, the radius from the bore hole to the outer periphery or boundary of the second fracture zones is much greater than the distance to the outer periphery or boundary of the first zone of fractured material from the bore hole. More specifically, the average furthest radially outward distance of the second fracture zones from the previously existing bore hole is much greater than the average radially outward distance of the fractured areas along the bore hole in the space between the spaced apart second zones.

More specifically, in one example the second fracture zones comprise a plurality of spaced apart rubblization discs of fractured geologic material. These discs extend outwardly to a greater radius than the radius of the first fracture zone. These discs can extend radially outwardly many times the distance of the first zones, such as six or more times as far.

By using non-ideal explosive formulations, less pulverization or powdering of rock adjacent to the previous existing bore hole results. Powdered pulverized rock can plug the desired fractures and interfere with the recovery of petroleum products (gas and oil) from such fracturing. The use of propellant charges and working fluid including working fluid in the bore hole outside of the explosive charges can assist in the reduction of this pulverization.

Specific exemplary approaches for implementing the methodology are described below. Any and all combinations and sub-combinations of these specific examples are within the scope of this disclosure.

Thus, in accordance with this disclosure, a plurality of spaced apart explosive charges can be positioned adjacent to one another along a section of the bore hole to be fractured. These adjacent explosive charges can be positioned in pairs of adjacent explosive charges with the explosive charges of each pair being arranged in an end to end relationship. The charges can be detonated together or at independent times. In one desirable approach, the charges are detonated such that detonation occurs at the end of the first of the pair of charges that is adjacent to the end of the second of the pair of charges that is also detonated. In yet another example, the detonation of the explosive charges only occurs at the respective adjacent ends of the pair of charges. Multiple pairs of these charges can be assembled in a string with or without propellant charges and working liquid containers positioned therebetween. Also, elongated propellant charges can be initiated from opposite ends of such propellant charges and can be assembled in plural propellant charge tubes. These propellant charge tube assemblies can be positioned intermediate to at least some of the explosive charges, or explosive charge assemblies. In accordance with another aspect of an example, pairs of explosive charges can be positioned as intercoupled charges in end to end relationships with a coupling therebetween. Pairs of propellant charges can be arranged in the same manner.

In an alternative embodiment, although expected to be less effective, a plurality of spaced apart propellant charges and assemblies of plural propellant charges can be initiated, with or without inert material containing tubes therebetween, with the explosive charges eliminated. In this case, the rubblization zones are expected to be less pronounced than rubblization zones produced with explosive charges, and with explosive charge and propellant charge combinations, with or without the inert material containers therebetween.

Other aspects of method acts and steps are found elsewhere in this disclosure. This disclosure encompasses all novel and non-obvious combinations and sub-combinations of method acts set forth herein.

VIII. Exemplary Detonation Results

FIG. 19 showsexemplary shock patterns500a,500b, and500cresulting from detonation of anexemplary string502 within a bore (not shown) in a geologic formation. Thestring502 comprises afirst HE system504a, asecond HE system504b, and athird HE system504c, and twoPP systems506 positioned between the three HE systems. Each of the HE systems504 is similar in construction and function to theexemplary HE system200 shown inFIGS. 12-14, and comprises a pair of HE units and a connector. ThePP systems506 comprise a pair of PP units and three adjacent connectors. TheHE system504ais centered on a causes theshock pattern500a, theHE system504bis centered on a causes theshock pattern500b, and theHE system504cis centered on a causes theshock pattern500c.

Taking theHE unit504aand its resultingshock pattern500aas an example, each of theindividual HE units510,512 causes nearlyidentical shock patterns514,516, respectively, that are symmetrical about theconnector518 that joins the HE units. Note that the illustrated shock pattern inFIG. 19 only shows a central portion of the resulting shock pattern from each HE system, and excludes portions of the shock pattern not between the centers of the two HE units. The portion of the shock pattern shown is of interest because the shocks from each of the two HE units interact with each other at a plane centered on theconnector518 between the two HE units, causing a significantsynergistic shock pattern520 that extends much further radially away from the bore and string compared to theindividual shock patterns514,516 of each HE unit.

By spacing the HE charges appropriately there results a zone of interaction between the charges which leads to a longer effective radius of shock and rubblization. Spaced and timed charges can increase the effected radius by a factor of 3 to 4 when compared to a single large explosive detonation. Instead of a dominate fracture being created that extends in a planar manner from the wellbore, the disclosed system can result in an entire volume rubblization that surrounds the wellbore in a full 360 degrees. In addition, possible radial fracturing that extends beyond the rubblized zone can result.

The HE charges can be separated by a distance determined by the properties of the explosive material and the surrounding geologic formation properties that allows for the development and interaction of release waves (i.e., unloading waves which occur behind the “front”) from the HE charges. A release wave has the effect of placing the volume of material into tension, and the coalescence of waves from adjacent charges enhances this tensile state. Consideration of the fact that rock fracture is favored in a state of tension, an exemplary multiple charge system favors optimum rock fracture by placing the rock in tension and enhancing the tensile state with the coalescence of waves from adjacent changes. Further, these fractures can remain open by self-propping due to asperities in the fracture surface.

Furthermore, the space between the HE charges includes PP systems. The PP systems cause additional stress state in the rock to enhance the effect of the main explosive charges.

FIG. 20 shows exemplary simulated results of a detonation as described herein. Two 2 meter long HE units, labeled600 and602, are connected in a HE system with an intermediate connector, and have a center-to-center separation L₁of 3.5 m. The HE system is detonated in abore604 in a theoretically uniform rock formation. The contours are rock fracture level, withzone20 representing substantially full rock fracture and zone X showing no fracture or partial fracture. Expected damage regions directly opposite each charge are apparent, and these extend to about 3 meters radially from thebore604. However, the region of the symmetry between the two charges shows a “rubble disk”606 that extends considerably further to a distance R₁, e.g., about 10 m, from the bore into the geologic formation. This simulation illustrates the extent of improved permeability through rock fracture that can be accomplished by taking advantage of shock wave propagation effects and charge-on-charge release wave interaction. Also, it is anticipated that late-time formation relaxation will induce additional fracturing between rubble disks.FIG. 20 is actually a slice through a 360° damage volume created about the axis of the charges.

In addition to the interaction between two adjacent charges, performance can be further improved by using an HE system with more than two HE units in series. For example,FIG. 21 shows three rubble disks created by four separated HE units, A, B, C, D. As inFIG. 20,FIG. 21 shows a slice through a 360° rubble zone.

Additional considerations in the design of explosive stimulation systems, such as described herein, can include the material and configuration of the HE unit container (e.g., aluminum tube), the inclusion of propellant units within the string in the axial volume between the individual charges, and the introduction of brine or other borehole fluid to fill the annulus separating the explosive system and the host rock formation. The propellant has been shown to be effective in boosting and extending the duration of the higher rock stress state, consequently extending fracture extent. The HE unit container can be designed not simply to facilitate placement of the system into a wellbore but, along with the wellbore fluid, it can provide a means for mechanically coupling the blast energy to the surrounding rock. Moreover, coupling of the shock through the aluminum or similar material case avoids short-duration shock which can result in near-wellbore crushing of the rock, with accompanying diminishment of available energy available for the desired long-range tensile fracturing process. This coupling phenomenon is complementary to the energy release characteristics of the explosive as discussed elsewhere herein.

The disclosed systems and numerical simulations can include consideration of site geologic layering and other properties. The seismic impedance contrast between two material types can create additional release waves in the shock environment. For example, an interlayered stiff sandstone/soft shale site can be modeled. The resulting environment predicted for a hypothetical layered site subjected to a two-explosive stimulation is shown inFIGS. 22A-22C. As in previous figures, these figures again show a slice through a 360° rubble zone.

FIGS. 22A-22C do not show a final predicted state (i.e., not full extent of fracturing), but show a point in time chosen to be illustrative of the phenomenology related to geologic layering.FIG. 22A is a contour of rock stress, with high stress regions “a” and low stress regions “b”.FIG. 22B displays the volume of fractured material, with zone “c” referring to fully fractured rock and transitioning to zone “d” where the material is in incipient fracture state, and zone “e” where there is no fracture.FIG. 22C displays the same material volume as inFIG. 22B, but material changes between sandstone in zone “g” and shale in zone “h” are shown.FIGS. 22A-22C illustrate that rubblization disks that can be produced in specific geologic locations with reference to the corresponding geologic layers by properly designed charge length and spacing based on known geologic properties. For example, inFIG. 22C, a majority of the rubblization is confined to the shale regions “g” and away from the sandstone region “h”.

IX. Exemplary Chemical Compositions

Chemical compositions disclosed herein are developed to optimize for cylinder energy. Such compositions are developed to provide different chemical environments as well as variation in temperature and pressure according to the desired properties, such as according to the specific properties of the geologic formation in which energy resources are to be extracted.

Compositions disclosed herein can include explosive material, also called an explosive. An explosive material is a reactive substance that contains a large amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material. This potential energy stored in an explosive material may be chemical energy, such as nitroglycerin or grain dust, pressurized gas, such as a gas cylinder or aerosol can. In some examples, compositions include high performance explosive materials. A high performance explosive is one which generates an explosive shock front which propagates through a material at supersonic speed, i.e. causing a detonation, in contrast to a low performance explosive which instead causes deflagration. In some examples, compositions include one or more insensitive explosives. Compositions disclosed herein can also include one or more propellants. In some examples, a propellant includes inert materials, such as brine, water, and mud, and/or energetic materials, such as explosive, combustible, and/or chemically reactive materials, or combinations thereof.

It is contemplated that a disclosed unit can include any explosive capable of creating a desired rubblization zones. Compositions which may be used in a disclosed unit are provided, but are not limited to, U.S. Pat. Nos. 4,376,083, 5,316,600, 6,997,996, 8,168,016, and 6,875,294 and USH1459 (United States Statutory Invention Registration, Jul. 4, 1995—High energy explosives).

In some examples, a composition includes a high-energy density explosive, such as comprising at least 8 kJ/cc, at least 10 kJ/cc, or at least 12 kJ/cc. In some examples, the explosive is a cast-cured formulation. In some examples, the explosive is a pressed powder (plastic bonded or otherwise), melt-cast, water gels/slurries and/or liquid. In some cases thermally stable explosives are included due to high-temperatures in certain geological formations. In some examples, non-nitrate/nitrate ester explosives (such as, AN, NG, PETN, ETN, EGDN) are used for these formulations, such as HMX, RDX, TATB, NQ, FOX-7, and/or DAAF. In some examples, explosive compositions include binder systems, such as binder systems substantially free of nitrate ester plasticizers. For example, suitable binder systems can include fluoropolymers, GAP, polybutadiene based rubbers or mixtures thereof. In some examples, explosive compositions include one or more oxidizers, such as those having the anions perchlorate, chlorate, nitrate, dinitramide, or nitroformate and cations, such as ammonium, methylammonium, hydrazinium, guanidinium, aminoguanidinium, diaminoguanidinium, triaminoguanidinium, Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba can be blended with the explosive to help oxidize detonation products. These can be of particular utility with fuel-rich binders are used such as polybutadiene based systems.

In some examples, the disclosed chemical compositions are designed to yield an energy density being greater than or equal to 8, 10, or 12 kJ/cc at theoretical maximum density, the time scale of the energy release being in two periods of the detonation phase with a large amount, greater than 25%, such as greater than 30% to 40%, being in the Taylor expansion wave and the produced explosive being a high density cast-cured formulation.

In some examples, the disclosed chemical compositions include one or more propellants. Propellant charges can be produced from various compositions used commonly in the field, being cast-cured, melt-cast, pressed or liquid, and of the general families of single, double or triple base or composite propellants. For example, a disclosed propellant unit comprises one or more oxidizers such as those having the anions perchlorate, chlorate, nitrate, dinitramide, or nitroformate and cations such as ammonium, methylammonium, hydrazinium, guanidinium, aminoguanidinium, diaminoguanidinium, triaminoguanidinium, Li, Na, K, Rb, Cs, Mg, Ca, Sr, and Ba. A propellant unit can also comprise one or more binders, such as one or more commonly used by one of ordinary skill in the art, such as polybutadiene, polyurethanes, perfluoropolyethers, fluorocarbons, polybutadiene acrylonitrile, asphalt, polyethylene glycol, GAP, PGN, AMMO/BAMO, based systems with various functionally for curing such as hydroxyl, carboxyl, 1,2,3-triazole cross-linkages or epoxies. Additives, such as transistion metal salt, for burning rate modification can also be included within a propellant unit. In some examples, one or more high-energy explosive materials are included, such as those from the nitramine, nitrate ester, nitroaromatic, nitroalkane or furazan/furoxan families. In some examples, a propellant unit also includes metal/semimetal additives such as Al, Mg, Ti, Si, B, Ta, Zr, and/or Hf which can be present at various particle sizes and morphologies.

In some examples, chemical compositions include one or more high-performance explosives (for example, but not limited to HMX, TNAZ, RDX, or CL-20), one or more insensitive explosives (TATB, DAAF, NTO, LAX-112, or FOX-7), one or more metals/semimetals (including, but not limited to Mg, Ti, Si, B, Ta, Zr, Hf or Al) and one or more reactive cast-cured binders (such as glycidyl azide(GAP)/nitrate (PGN) polymers, polyethylene glycol, or perfluoropolyether derivatives with plasitisizers, such as GAP plastisizer, nitrate esters or liquid fluorocarbons). While Al is the primary metal of the disclosed compositions it is contemplated that it can be substituted with other similar metals/semimetals such as Mg, Ti, Si, B, Ta, Zr, and/or Hf. In some examples, Al is substituted with Si and/or B. Si is known to reduce the sensitivity of compositions compared to Al with nearly the same heat of combustion. It is contemplated that alloys and/or intermetallic mixtures of above metals/semimetals can also be utilized. It is further contemplated that particle sizes of the metal/semi-metal additives can range from 30 nm to 40 μm, such as from 34 nm to 40 μm, 100 nm to 30 μm, 1 μm to 40 μm, or 20 μm to 35 μm. In some examples, particle sizes of the metal/semi-metal additives are at least 30 nm, at least 40 nm, at least 50 nm, at least 100 nm, at least 150 nm, at least 200 nm, at least 300 nm, at least 400 nm, at least 500 nm, at least 600 nm, at least 700 nm, at least 800 nm, at least 900 nm, at least 1 μm, at least 5 μm, at least 10 μm, at least 20 μm, at least 30 μm, including 30 nm, 40 nm, 50 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, or 40 μm. It is contemplated that the shape of particles may vary, such as atomized spheres, flakes or sponge morphologies. It is contemplated that the percent or combination of high-performance explosives, insensitive explosives, metals/semimetals and/or reactive cast-cured binders may vary depending upon the properties desired.

In some examples, a disclosed formulation includes about 50% to about 90% high-performance explosives, such as about 60% to about 80%, including 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90% high-performance explosives; about 0% to about 30% insensitive explosives, such as about 10% to about 20%, including 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% insensitive explosives; about 5% to about 30% metals or semimetals, such as about 10% to about 20%, including 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% metals/semimetals; and about 5% to about 30% reactive cast-cured binders, such as about 10% to about 20%, including 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% reactive cast-cured binders.

In some examples, a disclosed formulation includes about 50% to about 90% HMX, TNAZ, RDX and/or CL-20, such as about 60% to about 80%, including 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90% HMX, TNAZ, RDX and/or CL-20; about 0% to about 30% TATB, DAAF, NTO, LAX-112, and/or FOX-7, such as about 10% to about 20%, including 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% TATB, DAAF, NTO, LAX-112, and/or FOX-7; about 5% to about 30% Mg, Ti, Si, B, Ta, Zr, Hf and/or Al, such as about 10% to about 20%, including 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% Mg, Ti, Si, B, Ta, Zr, Hf and/or Al; and about 5% to about 30% glycidyl azide(GAP)/nitrate (PGN) polymers, polyethylene glycol, and perfluoropolyether derivatives with plasitisizers, such as GAP plastisizer, nitrate esters or liquid fluorocarbons, such as about 10% to about 20%, including 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% glycidyl azide(GAP)/nitrate (PGN) polymers, polyethylene glycol, and perfluoropolyether derivatives with plasitisizers, such as GAP plastisizer, nitrate esters or liquid fluorocarbons.

In some examples, a disclosed formulation includes about 50% to about 90% HMX, such as about 60% to about 80%, including 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90% HMX; about 0% to about 30% Al, such as about 10% to about 20%, including 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30% Al (with a particle size ranging from 30 nm to 40 μm, such as from 34 nm to 40 μm, 100 nm to 30 μm, 1 μm to 40 μm, or 20 μm to 35 μm. In some examples, particle sizes of the metal/semi-metal additives are at least 30 nm, at least 40 nm, at least 50 nm, at least 100 nm, at least 150 nm, at least 200 nm, at least 300 nm, at least 400 nm, at least 500 nm, at least 600 nm, at least 700 nm, at least 800 nm, at least 900 nm, at least 1 μm, at least 5 μm, at least 10 μm, at least 20 μm, at least 30 μm, including 30 nm, 40 nm, 50 nm, 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, or 40 μm); about 5% to about 15% glycidal azide polymer, such as about 7.5% to about 10%, including 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% glycidal azide polymer; about 5% to about 15% Fomblin Fluorolink D, such as about 7.5% to about 10%, including 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15% Fomblin Fluorolink D; and about 0% to about 5% methylene diphenyl diisocyanate, such as about 2% to about 4%, including 1%, 2%, 3%, 4%, or 5% methylene diphenyl diisocyanate.

In some examples, a disclosed composition includes at least a highly non-ideal HE is defined as an HE in which 30% to 40% or more of the meta-stably stored chemical energy is converted to HE hot products gases after the detonation front (shock front) in a deflagrating Taylor wave. In some examples, a disclosed composition does not include an ideal HE.

In some examples, a disclosed composition, such as a composition optimized for performance and thermal stability includes HMX, fluoropolymer and/or an energetic polymer (e.g., GAP) and Al. In some examples, other optimized formulations for performance and thermal stability can replace HMX with RDX for reduced cost mixture that also contains a fluoropolymer and/or energetic polymer (e.g., GAP) and Al.

In some examples, a disclosed composition includes 69% HMX, 15% 3.5 μm atomized Al, 7.5% glycidal azide polymer, 7.5% Fomblin Fluorolink D and 1% methylene diphenyl diisocyanate (having an mechanical energy of 12.5 kJ/cc at TMD).

In some examples, an inert surrogate is substituted for Al. In some examples, lithium fluoride (LiF) is one such material that may be substituted in certain formulations as an inert surrogate for Al. Other compounds which have a similar density, molecular weight and very low heat of formation so that it can be considered inert even in extreme circumstances may be substituted for Al. It is contemplated that the percentage of Al to the inert surrogate may range from about 10% Al to about 90% inert surrogate to about 90% Al and 10% inert surrogate. Such compositions may be used to develop models for metal reactions that extend beyond the current temperature and pressures in existing models.

EXAMPLESExample 1Explosive Compositions

This example discloses explosive compositions which can be used for multiple purposes, including fracturing.

Background:

Explosive regimes can be divided into three basic temporal stages: reaction in the CJ plane (very prompt reaction in the detonation, ns-μs), reaction in the post-detonation early expansion phase (4-10 μs) and late reaction to contribute to blast effects (1-100's of ms). Work on mixtures of TNT and Al (tritonals) began as early as 1914 and by WWII, where U.S. and British researchers discovered great effects in the third temporal regime of blast and no effects or detrimental effect to the prompt detonation regime. Because of a lack of acceleration in detonation wave speed, it is a commonly held belief in the energetics community that there is no Al participation at the C-J plane. However, some work has demonstrated that replacement of Al with an inert surrogate (NaCl) actually increased detonation velocity as compared to active Al, much more even than endothermic phase change could account for, therefore it was postulated that the Al does react in the C-J plane, however it is kinetically limited to endothermic reactions. In contrast, later work did not see as significant a difference in detonation velocity when Al was substituted for an inert surrogate (LiF) in TNT/RDX admixtures. However, this work showed a 55% increase in cylinder wall velocity for late-time expansion for the active Al versus surrogate, with Al contribution roughly 4 μs after the passage of the C-J plane.

Modern high performance munitions applications typically contain explosives, such as PBXN-14 or PBX9501, designed to provide short-lived high-pressure pulses for prompt structural damage or metal pushing. Another class of explosives, however, includes those that are designed for longer-lived blast output (enhanced blast) via late-time metal-air or metal detonation-product reactions. An example of an enhanced blast explosive, PBXN-109, contains only 64% RDX (cyclotrimethylenetrinitramine), and includes Al particles as a fuel, bound by 16% rubbery polymeric binder. The low % RDX results in diminished detonation performance, but later time Al/binder burning produces increased air blast. Almost in a separate class, are “thermobaric” type explosives, in which the metal loading can range from 30% to even as high as 90%. These explosives are different from the materials required for the present disclosure, as with such high metal loading, they are far from stoichiometric in terms of metal oxidation with detonation products, and additionally detonation temperature and pressure are considerably lower, which also effect metal oxidation rates. Therefore, such materials are well suited for late-time blast and thermal effects, but not for energy release in the Taylor expansion wave. Formulations combining the favorable initial work output from the early pressure profile of a detonation wave with late-time burning or blast are exceedingly rare and rely on specific ratios of metal to explosive as well as metal type/morphology and binder type. It has been demonstrated that both high metal pushing capability and high blast ability are achieved in pressed formulations by combining small size Al particles, conventional high explosive crystals, and reactive polymer binders. This combination is believed to be effective because the small particles of Al enhance the kinetic rates associated with diffusion-controlled chemistry, but furthermore, the ratio of Al to explosive was found to be of the utmost importance. It was empirically discovered that at levels of 20 wt % Al, the metal reactions did not contribute to cylinder wall velocity. This result is not only counterintuitive, but also is an indication that for metal acceleration applications, the bulk of current explosives containing Al are far from optimal. To fully optimize this type of combined effects explosive, a system in which the binder is all energetic/reactive, or completely replaced with a high performance explosive is needed. Furthermore, very little is understood about the reaction of Si and B in post-detonation environments.

Measurements:

In order to interrogate the interplay between prompt chemical reactions and Al combustion in the temporal reactive structure, as depicted in FIG. R, various measurement techniques are applied. Quantitative measurements in the microsecond time regime at high temperatures and pressures to determine the extent of metal reactions are challenging, and have been mostly unexplored to date. Techniques such as emission spectroscopy have been applied with success for observation of late-time metal oxidation, but the physiochemical environment and sub-microsecond time regime of interest in this study renders these techniques impractical. However, using a number of advanced techniques in Weapons Experiment Division, such as photon doppler velocimetry (PDV) and novel blast measurements, the initiation and detonation/burning responses of these new materials are probed. Predictions of the heats of reaction and detonation characteristics using modern thermochemical codes are used to guide the formulations and comparisons of theoretical values versus measured can give accurate estimations of the kinetics of the metal reactions. From measurement of the acceleration profile of metals with the explosives product gases, the pressure-volume relationship on an isentrope can be fit and is represented in the general form in equation 1, represented as a sum of functions over a range of pressures, one form being the JWL,equation 2.
P_SΣϕ(v)  (eq 1)
P_S=Ae^−R1V+Be^−R2V+CV^−(ω+1)  (eq 2)
In the JWL EOS, the terms A, B, C, R₁, R₂and ω are all constants that are calibrated, and V=v/v_o(which is modeled using hydrocodes). With thermochemically predicted EOS parameters, and the calibrated EOS from tested measurements, both the extent and the timing of metal reactions is accurately be accessed, and utilized for both optimization of formulations as well as in munitions design. The time-scale of this indirect observation of metal reactions dramatically exceeds what is possible from that of direct measurements, such as spectroscopic techniques. The formulations are then optimized by varying the amount, type and particle sizes of metals to both enhance the reaction kinetics, as well as tailor the time regime of energy output. Traditional or miniature versions of cylinder expansion tests are applied to test down selected formulations. Coupled with novel blast measurement techniques, the proposed testing will provide a quantitative, thorough understanding of metal reactions in PAX and cast-cured explosives to provide combined effects with a number of potential applications.

Formulation:

Chemical formulations are developed to optimize for cylinder energy. Such formulations are developed to provide different chemical environments as well as variation in temperature and pressure. Chemical formulations may include high-performance explosives (for example but not limited to HMX, TNAZ, RDX CL-20), insensitive explosives (TATB, DAAF, NTO, LAX-112, FOX-7), metals/semimetals (Al, Si or B) and reactive cast-cured binders (such as glycidyl azide(GAP)/nitrate (PGN) polymers, polyethylene glycol, and perfluoropolyether derivatives with plasitisizers such as GAP plastisizer, nitrate esters or liquid fluorocarbons). While Al is the primary metal of the disclosed compositions it is contemplated that it can be substituted with Si and/or B. Si is known to reduce the sensitivity of formulations compared to Al with nearly the same heat of combustion.

In order to verify thermoequlibrium calculations at a theoretical state or zero Al reaction, an inert surrogate for Al is identified. Lithium fluoride (LiF) is one such material that may be substituted in certain formulations as an inert surrogate for Al. The density of LiF is a very close density match for Al (2.64 gcm⁻³for LiF vs 2.70 gcm⁻³for Al), the molecular weight, 25.94 gmol⁻¹, is very close to that of Al, 26.98 gmol⁻¹, and it has a very low heat of formation so that it can be considered inert even in extreme circumstances. Because of these properties, LiF is believed to give formulations with near identical densities, particle size distributions, product gas molecular weights and yet give inert character in the EOS measurements. Initial formulations are produced with 50% and 100% LiF replacing Al. An understanding of reaction rates in these environments are used to develop models for metal reactions that extend beyond the current temperature and pressures in existing models.

Resulting material may be cast-cured, reducing cost and eliminating the infrastructure required for either pressing or melt-casting.

Particular Explosive Formulation

In one particular example, an explosive formulation was generated with an energy density being greater than or equal to 12 kJ/cc at theoretical maximum density, the time scale of the energy release being in two periods of the detonation phase with a large amount, greater than 30%, being in the Taylor expansion wave and the produced explosive being a high density cast-cured formulation. A formulation was developed and tested, which contained 69% HMX, 15% 3.5 μm atomized Al, 7.5% glycidal azide polymer, 7.5% Fomblin Fluorolink D and 1% methylene diphenyl diisocyanate (having an mechanical energy of 12.5 kJ/cc at TMD).

FIG. 23 provides a graphic depiction of a detonation structure of an explosive containing Al reacted or unreacted following flow-Taylor wave. Total mechanical energy in the formulation was equal to or greater than 12 kJ/cc. Greater than 30% of the energy was released in the following flow Taylor Wave of the explosive reaction due to reaction of Al (or other metals or semi-metals such as but not limited to Mg, Ti, Si, B, Ta, Zr, Hf). In the demonstrated explosive, 30-40% of energy was released in the Taylor Wave portion of the reaction. Other similar formulations similar to the above, but with a HTBP based non-reactive binder, failed to show early Al reaction in expansion. Further, formulations with nitrate ester plastisizers and added oxidizer failed to pass required sensitivity tests for safe handling.

Example 2Use of a Non-Ideal High Explosive (HE) System to Create Fracturing In-Situ within Geologic Formations

This example demonstrates the capability of the disclosed non-ideal HE system to be used to create fracturing in-situ within geologic formations.

Experimental/theoretical characterization of the non-ideal HE system was accomplished. The conceptual approach developed to the explosive stimulation of a nominal reservoir began with a pair of explosive charges in the wellbore separated by a distance determined by the properties of the explosive and the surrounding reservoir rock. The separation was the least required to assure that the initial outward going pressure pulse has developed a release wave (decaying pressure) behind was prior to the intersection of the two waves. The volume of material immediately behind the (nominally) circular locus of point where the intersecting waves just passed are loading in tension, favoring the fracture of the rock. The predicted result was a disc of fracture rock being generated out from the wellbore about midway between the charges. Numerical simulation supported this concept.FIG. 20 represents this result, as discussed above. In the center, along the plane of symmetry, the predicted effect of the two wave interaction was seen, projecting damage significantly further radially. The dimensions on this figure are for a particular computational trial, modeling a typical tight gas reservoir rock and are not to be inferred as more than illustrative.

Numeric models to represent the non-ideal HE system were built. Potential target reservoirs were identified, together with existing geophysical characterization of the representative formations. Numerical models to represent these formations were implemented. Numerical simulations indicating potential rubblized regions produced by multiple precision detonation events were calculated. Initial production modeling was conducted. Initial simulations indicated a rubblized region extending 20-30 feet in radius from the borehole.

FIGS. 24 and 25 illustrate gas production by conventional fracture (solid lines) and rubblized zone (dashed lines) from 250′ fractures with varying fracture conductivity or 3 cases of rubblized zones with radius of 20′, 24′ and 30′.

These studies demonstrate that the disclosed non-ideal HE system is a high energy density system which allows the zone affected by multiple timed detonation events to be extended by utilizing a “delayed” push in the energy in an environment of interacting shock/rarefaction waves. Moreover, the disclosed system allowed fracturing tight formations without hydraulically fracturing the formation.

In view of the many possible embodiments to which the principles disclosed herein may be applied, it should be recognized that illustrated embodiments are only examples and should not be considered a limitation on the scope of the disclosure. Rather, the scope of the disclosure is at least as broad as the scope of the following claims. We therefore claim all that comes within the scope of these claims.

Claims (20)

We claim:

1. An explosive unit for insertion into a borehole for use in fracturing a geologic formation surrounding the borehole, the explosive unit comprising:

a casing comprising a body defining an internal chamber;

a first component of an explosive positioned within the internal chamber of the casing;

at least one inlet communicating with the internal chamber through which a second component of the explosive is deliverable into the internal chamber to comprise the explosive;

wherein the casing comprises first and second opposed end caps and wherein at least one inlet tube extends from the at least one inlet through the first end cap, through the internal chamber, and through the second end cap, and wherein the at least one inlet tube delivers the second component of the explosive into the internal chamber.

2. The explosive unit ofclaim 1, wherein the first component comprises a liquid permeable oxidizer.

3. The explosive unit ofclaim 1, wherein the first component comprises a particulate solid material or a sponge-like material.

4. The explosive unit ofclaim 1, further comprising at least one remotely actuated vent communicating with the internal chamber.

5. The explosive unit ofclaim 1, wherein the at least one inlet tube comprises a tube with an inline outlet extending through the second end cap, an inlet extending through the first end cap and communicating with a source of the second component at a location that is remote from the explosive unit, and an internal outlet that communicates with the internal chamber.

6. An explosive system comprising an assembly of two or more elongated casings for insertion into a borehole for use in fracturing a geologic formation surrounding the borehole, the explosive system including:

a first elongated casing having a tubular body, first and second longitudinal end caps, and defining a first internal chamber;

a second elongated casing having a tubular body, first and second longitudinal end caps, and defining a second internal chamber, the first and second casings being mechanically coupled together in axial alignment;

each of the first and second casings comprising a first component of an explosive located within the respective internal chamber of the casing; and

at least one inlet tube communicating with the first and second internal chambers of the respective first and second casings, the at least one inlet tube being operable to deliver a second component of the explosive into the first and second internal chambers so as to combine with the first component of the explosive to comprise the explosive.

7. The system ofclaim 6, wherein the first component comprises a liquid permeable oxidizer and the second component comprises a liquid fuel.

8. The system ofclaim 6, wherein the at least one inlet tube comprises a first outlet communicating with the first internal chamber of the first casing and a second outlet communicating with the second internal chamber of the second casing.

9. The system ofclaim 6, wherein the at least one inlet tube comprises a first section extending from the first casing, a second section extending into the second casing, and an inlet tube coupler that couples the first and second inlet tube sections together between the first and second casings.

10. The system ofclaim 7, wherein a first end of the at least one inlet tube is coupled to a liquid fuel source configured to supply the liquid fuel through the at least one inlet tube into the first and second internal chambers.

11. The system ofclaim 10, wherein the first end of the at least one inlet tube is further coupled to a vacuum pump configured to create a vacuum within the first and second internal chambers so as to draw the liquid fuel into the internal chambers.

12. The system ofclaim 6, further comprising at least one outlet vent tube communicating with the first and second internal chambers and being operable to vent fluid from the first and second internal chambers when the second component of the explosive is delivered into the first and second internal chambers.

13. The system ofclaim 12, wherein the at least one inlet tube has no outlet within the first casing and has an outlet within the second internal chamber of the second casing, and comprising a passageway communicating from the second internal chamber to the first internal chamber.

14. The system ofclaim 13, wherein the second component of the explosive is configured to flow along the at least one inlet tube through the first casing, flow out of the outlet of the at least one inlet tube into the internal chamber of the second casing, flow into the passageway from the second internal chamber, and flow out of the passageway into the first internal chamber.

15. The system ofclaim 12, wherein the outlet tube comprises a first section extending from the second casing, a second section extending into the first casing, and an outlet tube coupler that couples the first and second outlet tube sections together between the first and second casings.

16. The system ofclaim 14, comprising at least one vent coupled to the internal chambers of the first and second casings, wherein the first component comprises a permeable oxidizer and the second component comprises a liquid fuel, and wherein the system comprises a pump that pumps the liquid through the at least one inlet tube, into the internal chamber of the second casing, and through the outlet tube into the first casing, and wherein the at least one vent tube vents the internal chambers as the liquid flows into the first and second chambers.

17. A method comprising:

inserting an explosive assembly into a wellbore, the assembly comprising a first explosive unit and a second explosive unit, each explosive unit having a casing with a first component of an explosive within the casing; and then

flowing a second component of the explosive into the inserted casings of the first and second explosive units using a common inlet tube extending through each casing to comprise the explosive within each explosive unit;

detonating the explosive to fracture the geologic structure surrounding the borehole and the casings.

18. A method according toclaim 17, wherein the act of flowing the second component comprises flowing the second component into the first explosive unit from a location outside of the entrance opening to the wellbore.

19. A method according toclaim 17, wherein the act of flowing comprises venting the casings and pumping the second component into the vented casings, and the method further comprises closing at least one vent following flowing of the second component into the casings.

20. A method according toclaim 17, wherein the act of flowing comprises drawing a vacuum within the casings, coupling a supply of the second component to the casings, and using the vacuum in the casings to draw the second component into the casings.

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